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[BUG] 2.4.3 SIGSEGV in fts_solr
by Nick O'Connor 01 Apr '26

01 Apr '26

Dovecot 2.4.3 crashes with SIGSEGV in indexer-worker and lmtp during FTS Solr indexing. The crash is a use-after-free triggered when the HTTP client does a DNS lookup for the Solr host. Environment: - Dovecot 2.4.3 (Alpine 3.23 / musl) - Linux x86_64 - Filesystem: maildir on ZFS - Solr 10.0.0 - fts_solr plugin with DNS-based Solr URL dovecot -n: # 2.4.3 (e278b1e09b): /etc/dovecot/dovecot.conf # Pigeonhole version 2.4.3 (0bf9ee48) # OS: Linux 6.12.74+deb13+1-amd64 x86_64 dovecot_config_version = 2.4.0 auth_mechanisms = oauthbearer xoauth2 dovecot_storage_version = 2.4.0 fts_autoindex = yes fts_search_add_missing = yes mail_always_cache_fields = date.save mail_driver = maildir mail_plugins { fts = yes fts_solr = yes } protocols = imap lmtp sieve ssl = required fts solr { url = http://solr.example.com/solr/dovecot } (LDAP userdb/passdb, pigeonhole sieve, imapsieve for spam learning, and oauth2 passdb omitted) How to reproduce: The crash occurs in the indexer-worker when processing multiple user mailboxes sequentially for FTS indexing, using a DNS hostname for the Solr URL. Steps: 1. Configure fts_solr with a DNS-based URL (not an IP address) 2. Have the indexer-worker process mailboxes for more than one user (e.g. fts_autoindex = yes with multiple users, or manual doveadm index -A) 3. The first user session completes successfully. On the second user session, the indexer-worker crashes with SIGSEGV during the DNS lookup for the Solr host. Reproduces reliably on musl (Alpine) due to aggressive memory reuse. Likely also affects glibc but may not crash immediately due to delayed reuse of freed memory. Root cause: The solr_http_client singleton outlives the user session that created it. Its event chain holds a ref on the mail_storage_service_user event, keeping it alive after the user is freed. The SETTINGS_EVENT_INSTANCE on that event still points to the already-freed settings_instance. On the next user session, dns_lookup() walks the stale event chain and dereferences the dangling pointer in settings_instance_get(). Stack trace (from core dump, debug build with musl-dbg): #0 strlen(s=0x415641d189485741) -- SIGSEGV, freed/reused memory #1 p_strdup() strfuncs.c:56 #2 event_add_str(key="protocol", value=...) lib-event.c:1099 #3 settings_instance_get() settings.c:2521 #4 settings_get_real() settings.c:2706 #5 settings_get_full() settings.c:2915 #6 settings_get(dns_client_setting_parser_info) settings.c:2976 #7 dns_client_init() dns-lookup.c:465 #8 dns_client_init_handle_failure() dns-lookup.c:317 #9 dns_lookup("solr.example.com") dns-lookup.c:337 #10 http_client_host_shared_lookup() http-client-host.c:166 #11 http_client_host_shared_refresh() http-client-host.c:195 #12-#19 http_client queue/host/request submit chain #20 http_client_request_continue_payload() http-client-request.c:1170 #21 http_client_request_send_payload() http-client-request.c:1261 #22 solr_connection_post_more() solr-connection.c:269 Proposed fix: Destroy solr_http_client in solr_connection_deinit() so it is recreated with a fresh event chain on the next user session: --- a/src/plugins/fts-solr/solr-connection.c +++ b/src/plugins/fts-solr/solr-connection.c @@ -117,6 +117,8 @@ void solr_connection_deinit(struct solr_connection **_conn) *_conn = NULL; event_unref(&conn->event); + if (solr_http_client != NULL) + http_client_deinit(&solr_http_client); i_free(conn->http_host); i_free(conn->http_base_url); I've been running for few days with the patch applied. FTS indexing across multiple user sessions completes without crashes using a DNS-based Solr URL. Please let me know if there's anything else that would be helpful. The core files have sensitive information so I've omitted them from the report. -Nick Dovecot 2.4.3 crashes with SIGSEGV in indexer-worker and lmtp during FTS Solr indexing. The crash is a use-after-free triggered when the HTTP client does a DNS lookup for the Solr host. Environment: - Dovecot 2.4.3 (Alpine 3.23 / musl) - Linux x86_64 - Filesystem: maildir on ZFS - Solr 10.0.0 - fts_solr plugin with DNS-based Solr URL dovecot -n: # 2.4.3 (e278b1e09b): /etc/dovecot/dovecot.conf # Pigeonhole version 2.4.3 (0bf9ee48) # OS: Linux 6.12.74+deb13+1-amd64 x86_64 dovecot_config_version = 2.4.0 auth_mechanisms = oauthbearer xoauth2 dovecot_storage_version = 2.4.0 fts_autoindex = yes fts_search_add_missing = yes mail_always_cache_fields = date.save mail_driver = maildir mail_plugins { fts = yes fts_solr = yes } protocols = imap lmtp sieve ssl = required fts solr { url = http://solr.example.com/solr/dovecot } (LDAP userdb/passdb, pigeonhole sieve, imapsieve for spam learning, and oauth2 passdb omitted) How to reproduce: The crash occurs in the indexer-worker when processing multiple user mailboxes sequentially for FTS indexing, using a DNS hostname for the Solr URL. Steps: 1. Configure fts_solr with a DNS-based URL (not an IP address) 2. Have the indexer-worker process mailboxes for more than one user (e.g. fts_autoindex = yes with multiple users, or manual doveadm index -A) 3. The first user session completes successfully. On the second user session, the indexer-worker crashes with SIGSEGV during the DNS lookup for the Solr host. Reproduces reliably on musl (Alpine) due to aggressive memory reuse. Likely also affects glibc but may not crash immediately due to delayed reuse of freed memory. Root cause: The solr_http_client singleton outlives the user session that created it. Its event chain holds a ref on the mail_storage_service_user event, keeping it alive after the user is freed. The SETTINGS_EVENT_INSTANCE on that event still points to the already-freed settings_instance. On the next user session, dns_lookup() walks the stale event chain and dereferences the dangling pointer in settings_instance_get(). Stack trace (from core dump, debug build with musl-dbg): #0 strlen(s=0x415641d189485741) -- SIGSEGV, freed/reused memory #1 p_strdup() strfuncs.c:56 #2 event_add_str(key="protocol", value=...) lib-event.c:1099 #3 settings_instance_get() settings.c:2521 #4 settings_get_real() settings.c:2706 #5 settings_get_full() settings.c:2915 #6 settings_get(dns_client_setting_parser_info) settings.c:2976 #7 dns_client_init() dns-lookup.c:465 #8 dns_clien t_init_handle_failure() dns-lookup.c:317 #9 dns_lookup("solr.example.com") dns-lookup.c:337 #10 http_client_host_shared_lookup() http-client-host.c:166 #11 http_client_host_shared_refresh() http-client-host.c:195 #12-#19 http_client queue/host/request submit chain #20 http_client_request_continue_payload() http-client-request.c:1170 #21 http_client_request_send_payload() http-client-request.c:1261 #22 solr_connection_post_more() solr-connection.c:269 Proposed fix: Destroy solr_http_client in solr_connection_deinit() so it is recreated with a fresh event chain on the next user session: --- a/src/plugins/fts-solr/solr-connection.c +++ b/src/plugins/fts-solr/solr-connection.c @@ -117,6 +117,8 @@ void solr_connection_deinit(struct solr_connection **_conn) *_conn = NULL; event_unref(&conn->event); + if (solr_http_client != NULL) + http_client_deinit(&solr_http_client); i_free(conn->http_host); i_free(conn->http_base_url); I've been running for few days with the patch applied. FTS indexing across multiple user sessions completes without crashes using a DNS-based Solr URL. Please let me know if there's anything else that would be helpful. The core files have sensitive information so I've omitted them from the report. -Nick

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migration from 2.3 to 2.4 : postfix can't deliver via lmtp
by Stefan G. Weichinger 31 Mar '26

31 Mar '26

I am in the process of upgrading and rewriting my config. I can access IMAP etc ... so my database access is working. I have issues with LMTP: postfix can't deliver to dovecot. The postfix-confiog wasn't touched at all. the error: Mar 27 11:46:37 co dovecot: auth(stefan(a)oops.co.at): Error: userdb: client doesn't have lookup permissions for this user: userdb reply doesn't contain uid (to bypass this check, set: service auth { unix_listener /run/dovecot/auth-userdb { mode=0777 } }) What I don't understand: I configure this: service auth { unix_listener /var/spool/postfix/private/auth { group = postfix mode = 0666 user = postfix } } service auth-worker { user = postfix } service lmtp { user = vmail unix_listener /var/spool/postfix/private/dovecot-lmtp { group = postfix mode = 0660 user = postfix } } protocol lmtp { mail_plugins = sieve postmaster_address = logs(a)xunil.at } And in postfix: virtual_transport = lmtp:unix:private/dovecot-lmtp virtual_uid_maps = static:5000 virtual_gid_maps = static:5000 local_transport = virtual local_recipient_maps = $virtual_mailbox_maps smtpd_sasl_auth_enable = yes smtpd_sasl_type = dovecot smtpd_sasl_path = private/auth Where does "/run/dovecot/auth-userdb" come from? I understand that according to my config /var/spool/postfix/private/auth should be used? ls /var/spool/postfix/private/auth -l srw-rw-rw- 1 postfix postfix 0 Mar 27 11:45 /var/spool/postfix/private/auth ls /var/spool/postfix/private/dovecot-lmtp -l srw-rw---- 1 postfix postfix 0 Mar 27 11:45 /var/spool/postfix/private/dovecot-lmtp I'd appreciate any quick help here ... while googling and testing around ... thanks!

2 17

upgrade to 2.4
by John Hill 31 Mar '26

31 Mar '26

Dovecot may go down as one of the best/worst software in its category. I'm staying on Debian 12 doing backports, till the dust settles several times. --john

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Fwd: dovecot mailing list probe message
by Jaco Kroon 30 Mar '26

30 Mar '26

Hi, It seems like the list system is breaking DKIM - triggering bounces, resulting in unsuscribes. Is there recommendations on how to deal with this? Looks like it relates 100% to the addition of the footer: ______________________________________________ dovecot mailing list -- dovecot(a)dovecot.org To unsubscribe send an email to dovecot-leave(a)dovecot.org Kind regards, Jaco -------- Forwarded Message -------- Subject: dovecot mailing list probe message Date: Mon, 30 Mar 2026 06:32:58 +0000 From: dovecot-bounces+a190cb9ae5d94d8fa6e2af68fc964a7aaa13256b(a)dovecot.org To: jaco(a)uls.co.za This is a probe message. You can ignore this message. The dovecot(a)dovecot.org mailing list has received a number of bounces from you, indicating that there may be a problem delivering messages to jaco(a)uls.co.za. A sample is attached below. Please examine this message to make sure there are no problems with your email address. You may want to check with your mail administrator for more help. You don't need to do anything to remain an enabled member of the mailing list. If you have any questions or problems, you can contact the mailing list owner at dovecot-owner(a)dovecot.org Hi, It seems like the list system is breaking DKIM - triggering bounces, resulting in unsuscribes. Is there recommendations on how to deal with this? Looks like it relates 100% to the addition of the footer: ______________________________________________ dovecot mailing list -- [1]dovecot(a)dovecot.org To unsubscribe send an email to [2]dovecot-leave(a)dovecot.org Kind regards, Jaco -------- Forwarded Message -------- Subject: dovecot mailing list probe message Date: Mon, 30 Mar 2026 06:32:58 +0000 From: [3]dovecot-bounces+a190cb9ae5d94d8fa6e2af68fc964a7aaa13256b(a)dovecot.org To: [4]jaco(a)uls.co.za This is a probe message. You can ignore this message. The [5]dovecot(a)dovecot.org mailing list has received a number of bounces from you, indicating that there may be a problem delivering messages to [6]jaco(a)uls.co.za. A sample is attached below. Please examine this message to make sure there are no problems with your email address. You may want to check with your mail administrator for more help. You don't need to do anything to remain an enabled member of the mailing list. If you have any questions or problems, you can contact the mailing list owner at [7]dovecot-owner(a)dovecot.org References Visible links 1. mailto:dovecot@dovecot.org 2. mailto:dovecot-leave@dovecot.org 3. mailto:dovecot-bounces+a190cb9ae5d94d8fa6e2af68fc964a7aaa13256b@dovecot.org 4. mailto:jaco@uls.co.za 5. mailto:dovecot@dovecot.org 6. mailto:jaco@uls.co.za 7. mailto:dovecot-owner@dovecot.org

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Update to v2.4.3 breaks ldap connection
by markus-dovecot＠doits.de 30 Mar '26

30 Mar '26

Unfortunately the upgrade to v2.4.3 broke the ldap connection. I have configured an ldap connection like this: ``` ldap_uris = ldaps://xxx.com ldap_auth_dn = uid=xxx,ou=general accounts,dc=xxx,dc=com ldap_auth_dn_password = xxx ldap_base = dc=xxx,dc=com passdb ldap { ldap_bind = yes [...] } ``` v2.4.3 cannot connect and says: ``` auth: Error: ldap(ldaps://xxx.com636): Can't connect to server: ldaps://xxx.com ``` Ldap server logs: ``` ACCEPT from IP=[XXX]:45674 (IP=[::]:636) TLS established tls_ssf=256 ssf=256 tls_proto=TLS1.3 tls_cipher=AES-256-GCM closed (connection lost) ``` Downgrade to dovecot v2.4.2 makes it work again. Was there any ldap change in v2.4.3 that required a config change? Using ubuntu 24.04 with the dovecot ppa, now forced version 2.4.2 by using https://repo.dovecot.org/ce-2.4.2/ubuntu/noble

4 6

Dovecot 2.4.3 virtual now broken even more
by sev monster 30 Mar '26

30 Mar '26

As of 2.4.2, Dovecot no longer crashed and broken config vars no longer caused it to error out, so I finally (reluctantly) switched to it over 2.3, though I had to disable/change a few things to get it to work. However, my virtual namespaces were still broken, since the `autosubscribe = yes` option would cause the driver to attempt to create the virtual directories, and fail when they already existed. Turning off autosubscribe meant that the folders were not visible to my users without manually subscribing. With 2.4.3, now the virtual configs that "worked" before now cause Dovecot to error out completely! Yay It seems this commit introduced a "feature" that restricts the virtual driver to the fs list format: https://github.com/dovecot/core/commit/b4a4a32361b8f0e68ef230add6467eddd0ff… But why? Is fs the only format that works? But maildir++ worked in both 2.3 and in previous versions of 2.4. The 2.4.3 docs (still) also recommend switching to maildir++ if desired: https://doc.dovecot.org/2.4.3/core/plugins/virtual.html#virtual-mailbox-plu… In my config, I use maildir for everything. That means in my mailboxes and all my namespaces. But with this change, I must now use fs as my list format for the virtuals. But, I can't do that, because all `list = yes` namespaces in use by a mailbox must use the same list format... So now my previously invisible virtual folders now cause Dovecot to fall over and I have to completely remove the virtual declarations from my config. What am I supposed to do now?

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Executing a sieve-extprograms pipe script as non-root
by Roland Hieber 29 Mar '26

29 Mar '26

Hi, Ultimately I'm trying to call procmail via a `pipe "procmail";` in my Sieve script on Dovecot 2.4.1. I have therefore created the respective wrapper script in /usr/lib/dovecot/sieve-pipe/procmail, but I noted that the script is apparently run as root. With some debug output in the wrapper script, I see: # `id` output uid=0(root) gid=1059(rhi) groups=1059(rhi),116(dovecot) # `pstree -s -u $$` systemd(1)---dovecot(1064)---lmtp(266577,rhi)---procmail(266706,root)---pstree(266711) This Dovecot gets mail delivered via LMTP from another server. 1059 (rhi) is my local user ID on the IMAP server both in /etc/passwd and in /etc/dovecot/users (using auth-passwdfile.conf.ext in 10-auth.conf instead of auth-system.conf.ext), since mail needs to be delivered and chown'ed correctly into Maildirs that should be user-accessible. However I don't understand how the `procmail` wrapper can be run as the root user rights when the LMTP process starting it is running as my own user?!? I'd like to prevent procmail from running as root as far as possible, so for now I've been able to work around this by wrapping the procmail call into an additional `sudo -U $USER` (after determining the user who owns the target maildir), but I'd like to understand the problem a bit further and like to know if this is really how calling sieve-extprograms is supposed to work – I'd have expected that the external scripts are also run as my unprivileged user. I'm running a fairly standard config on Debian stable (dovecot package version 1:2.4.1+dfsg1-6+deb13u2) with only minimal changes by enabling the passwdfile backend and some sieve plugins. Thanks for any insights, - Roland -- Roland Hieber, Pengutronix e.K. | rhi(a)pengutronix.de | Steuerwalder Str. 21 | https://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |

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dovecot 2.4.x director
by Maciej Milaszewski 27 Mar '26

27 Mar '26

HI Has anyone managed to create a fork or other solution that provides director functionality? A small setup where it can be managed, for example, with Rabit/Redis, is one thing, but not a larger environment. The documentation for 2.4.x seems to have something like this: https://doc.dovecot.org/2.4.3/howto/lua_director.html "This is an unsupported method of running Dovecot. Caveat emptor. It is only intended for small-scale deployments – this is NOT designed to scale for more than a few servers."

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Dovecot Security Advisory OXDC-2026-0001
by Aki Tuomi 27 Mar '26

27 Mar '26

Hi! We're sharing our latest advisory with you and like to thank everyone who contributed in finding and solving those vulnerabilities. This advisory is also published at https://documentation.open-xchange.com/dovecot/security/advisories/html/202… --- Internal reference: DOV-7830 Type: CWE-1250 (Improper Preservation of Consistency Between Independent Representations of Shared State) Component: core Report confidence: Confirmed Solution status: Fixed by vendor Last affected revision: OX Dovecot CE core 2.4.0 First fixed revision: OX Dovecot CE core 2.4.1 Discovery date: 2025-07-24 Solution date: 2026-03-27 Disclosure date: 2026-03-27 Researcher credits: Erik <erik(a)broadlux.com> CVE: CVE-2025-30189 CVSS: 7.4 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N) Details: v2.4 regression: auth cache broken with several passdb / userdb. When cache is enabled, some passdb/userdb drivers incorrectly cache all users with same cache key, causing wrong cached information to be used for these users. Risk: After cached login, all subsequent logins are for same user. No publicly available exploits are known. Solution: Install fixed version or disable caching either globally or for the impacted passdb/userdb drivers. --- Internal reference: DOV-8349 Type: CWE-20 (Improper Input Validation) Component: core Report confidence: Confirmed Solution status: Fixed by vendor Last affected revision: OX Dovecot CE core 2.4.0 First fixed revision: OX Dovecot CE core 2.4.3 Discovery date: 2025-11-04 Solution date: 2026-03-27 Disclosure date: 2026-03-27 CVE: CVE-2025-59028 CVSS: 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L) Details: Invalid base64 authentication can cause DoS for other logins. When sending invalid base64 SASL data, login process is disconnected from the auth server, causing all active authentication sessions to fail. Risk: Invalid BASE64 data can be used to DoS a vulnerable server to break concurrent logins. No publicly available exploits are known. Solution: Install fixed version or disable concurrency in login processes (heavy perfomance penalty on large deployments). --- Internal reference: DOV-8508 Type: CWE-20 (Improper Input Validation) Component: core Report confidence: Confirmed Solution status: Fixed by vendor Last affected revision: OX Dovecot CE core 2.4.0 First fixed revision: OX Dovecot CE core 2.4.3 Discovery date: 2025-11-29 Solution date: 2026-03-27 Disclosure date: 2026-03-27 CVE: CVE-2025-59032 CVSS: 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) Details: v2.4/v3.1 regression: Pigeonhole: ManageSieve panic occurs with sieve-connect as a client. ManageSieve AUTHENTICATE command crashes when using literal as SASL initial response. Risk: This can be used to crash ManageSieve service repeatedly, making it unavailable for other users. No publicly available exploits are known. Solution: Control access to ManageSieve port, or disable the service if it's not needed. Alternatively upgrade to a fixed version. --- Internal reference: DOV-8584 Type: CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor) Component: core Report confidence: Confirmed Solution status: Fixed by vendor Last affected revision: OX Dovecot Pro core 2.3.0 First fixed revision: OX Dovecot CE core 2.4.3 Discovery date: 2025-12-29 Solution date: 2026-03-27 Disclosure date: 2026-03-27 Researcher credits: cavid@yeswehack CVE: CVE-2025-59031 CVSS: 4.3 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N) Details: decode2text.sh OOXML extraction may follow symlinks and read unintended files during indexing. Dovecot has provided a script to use for attachment to text conversion. This script unsafely handles zip-style attachments. Risk: Attacker can use specially crafted OOXML documents to cause unintended files on the system to be indexed and subsequently ending up in FTS indexes. No publicly available exploits are known. Solution: Do not use the provided script, instead, use something else like FTS tika. --- Internal reference: DOV-8591 Type: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')) Component: core Report confidence: Confirmed Solution status: Fixed by vendor Last affected revision: OX Dovecot Pro core 2.3.0 First fixed revision: OX Dovecot CE core 2.4.0 Discovery date: 2026-01-07 Solution date: 2026-03-27 Disclosure date: 2026-03-27 Researcher credits: strokep@yeswehack CVE: CVE-2026-0394 CVSS: 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N) Details: auth: Path traversal in passwd-file passdb using `%d` (domain) escapes base directory and opens `/etc/passwd`Pre-auth path traversal in passwd-file passdb using `%d` (domain) escapes base directory and opens `/etc/passwd`. When dovecot has been configured to use per-domain passwd files, and they are placed one path component above /etc, or slash has been added to allowed characters, path traversal can happen if the domain component is directory partial. Risk: This allows inadvertently reading /etc/passwd (or some other path which ends with passwd). If this file contains passwords, it can be used to authenticate wrongly, or if this is userdb, it can unexpectly make system users appear valid users. No publicly available exploits are known. Solution: Upgrade to fixed version, or use different authentication scheme that does not rely on paths. Alternatively you can also ensure that the per-domain passwd files are in some other location, such as /etc/dovecot/auth/%d. --- Internal reference: DOV-8775 Type: CWE-90 (Improper Neutralization of Special Elements used in an LDAP Query ('LDAP Injection')) Component: core Report confidence: Confirmed Solution status: Fixed by vendor Last affected revision: OX Dovecot CE core 2.4.0 First fixed revision: OX Dovecot CE core 2.4.3 Discovery date: 2026-02-20 Solution date: 2026-03-27 Disclosure date: 2026-03-27 Researcher credits: cookiejack15@yeswehack CVE: CVE-2026-27860 CVSS: 3.7 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N) Details: v2.4/v3.1 regression: auth-ldap is not escaping usernames. If auth_username_chars is empty, it is possible to inject arbitrary LDAP filter to Dovecot's LDAP authentication. Risk: This leads to potentially bypassing restrictions and allows probing of LDAP structure. No publicly available exploits are known. Solution: Do not clear out auth_username_chars, or install fixed version. --- Internal reference: DOV-8781 Type: CWE-89 (Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection')) Component: core Report confidence: Confirmed Solution status: Fixed by vendor Last affected revision: OX Dovecot CE core 2.4.0 First fixed revision: OX Dovecot CE core 2.4.3 Discovery date: 2026-02-23 Solution date: 2026-03-27 Disclosure date: 2026-03-27 Researcher credits: whisperer@yeswehack CVE: CVE-2026-24031 CVSS: 7.7 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L) Details: v2.4/v3.1 regression: SQL injection allows bypassing authentication. Dovecot SQL based authentication can be bypassed when auth_username_chars is cleared by admin. Risk: This vulnerability allows bypassing authentication for any user and user enumeration. No publicly available exploits are known. Solution: Do not clear auth_username_chars. If this is not possible, install latest fixed version. --- Internal reference: DOV-8787 Type: CWE-400 (Uncontrolled Resource Consumption) Component: core Report confidence: Confirmed Solution status: Fixed by vendor Last affected revision: OX Dovecot CE core 2.4.0 First fixed revision: OX Dovecot CE core 2.4.3 Discovery date: 2026-02-24 Solution date: 2026-03-27 Disclosure date: 2026-03-27 Researcher credits: djvirus@yeswehack CVE: CVE-2026-27859 CVSS: 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L) Details: v3.0.2+ regression: Message headers MIME parameter parsing can cause excessive CPU usage. A mail message containing excessive amount of RFC 2231 MIME parameters causes LMTP to use too much CPU. Risk: A suitably formatted mail message causes mail delivery process to consume large amounts of CPU time. No publicly available exploits are known. Solution: Use MTA capabilities to limit RFC 2231 MIME parameters in mail messages, or upgrade to fixed version where the processing is limited. --- Internal reference: DOV-8816 Type: CWE-400 (Uncontrolled Resource Consumption) Component: core Report confidence: Confirmed Solution status: Fixed by vendor Last affected revision: OX Dovecot Pro core 2.3.0 First fixed revision: OX Dovecot CE core 2.4.3 Discovery date: 2026-02-27 Solution date: 2026-03-27 Disclosure date: 2026-03-27 Researcher credits: whisperer@yeswehack CVE: CVE-2026-27857 CVSS: 4.3 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L) Details: imap-login: Excessive memory usage DoS. Sending "NOOP (((...)))" command with 4000 parenthesis open+close results in ~1MB extra memory usage. Longer commands will result in client disconnection. This 1 MB can be left allocated for longer time periods by not sending the command ending LF. So attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Risk: Attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. No publicly available exploits are known. Solution: Install fixed version, there is no other remediation. --- Internal reference: DOV-8818 Type: CWE-400 (Uncontrolled Resource Consumption) Component: core Report confidence: Confirmed Solution status: Fixed by vendor Last affected revision: OX Dovecot Pro core 2.3.0, OX Dovecot CE core 2.4.0 First fixed revision: OX Dovecot CE core 2.4.3 Discovery date: 2026-02-28 Solution date: 2026-03-27 Disclosure date: 2026-03-27 Researcher credits: ilyar@yeswehack CVE: CVE-2026-27858 CVSS: 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) Details: managesieve-login out-of-memory DoS. Attacker can send a specifically crafted message before authentication that causes managesieve to allocate large amount of memory. Risk: Attacker can force managesieve-login to be unavailable by repeatedly crashing the process. No publicly available exploits are known. Solution: Protect access to managesieve protocol, or install fixed version. --- Internal reference: DOV-8830 Type: CWE-287 (Improper Authentication) Component: core Report confidence: Confirmed Solution status: Fixed by vendor Last affected revision: OX Dovecot Pro core 2.3.0 First fixed revision: OX Dovecot CE core 2.4.3 Discovery date: 2026-03-04 Solution date: 2026-03-27 Disclosure date: 2026-03-27 Researcher credits: bksparajuli@yeswehack CVE: CVE-2026-27856 CVSS: 7.4 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N) Details: doveadm: Credentials verified without timing safety. Doveadm credentials are verified using direct comparison which is susceptible to timing oracle attack. An attacker can use this to determine the configured credentials. Risk: Figuring out the credential will lead into full access to the affected component. No publicly available exploits are known. Solution: Limit access to the doveadm http service port, install fixed version. --- Internal reference: DOV-8859 Type: CWE-294 (Authentication Bypass by Capture-replay) Component: core Report confidence: Confirmed Solution status: Fixed by vendor Last affected revision: OX Dovecot Pro core 2.3.0 First fixed revision: OX Dovecot CE core 2.4.3 Discovery date: 2026-03-09 Solution date: 2026-03-27 Disclosure date: 2026-03-27 Researcher credits: hamizanazman@yeswehack CVE: CVE-2026-27855 CVSS: 6.8 (CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N) Details: auth: OTP driver vulnerable to replay attack. Dovecot OTP authentication is vulnerable to replay attack under specific conditions. If auth cache is enabled, and username is altered in passdb, then OTP credentials can be cached so that same OTP reply is valid. Risk: An attacker able to observe an OTP exchange is able to log in as the user. No publicly available exploits are known. Solution: If authentication happens over unsecure connection, switch to SCRAM protocol. Alternatively ensure the communcations are secured, and if possible switch to OAUTH2 or SCRAM.

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Imap Sieve errors in 2.4.2
by Alberto 26 Mar '26

26 Mar '26

Hi, I have a Dovecot docker image with last version (2.4.2). I'm getting some errors, last time a few minutes ago, when dragging some emails into a folder I had just created. ... Mar 26 10:48:20 imap(alberto(a)bersol.info)<451><wHkgJepNsLRYDtBg>: Info: Mailbox INBOX.carpetanueva: Mailbox created Mar 26 10:48:24 imap(alberto(a)bersol.info)<397><x8N6YuhNMs9YDtBg>: Panic: file imap-sieve-storage.c: line 216 (imap_sieve_add_mailbox_event): assertion failed : (ismt->src_box == NULL || ismt->src_box == src_box) Mar 26 10:48:24 imap(alberto(a)bersol.info)<397><x8N6YuhNMs9YDtBg>: Error: Raw backtrace: #1 [unw_get_proc_name() failed: -10] -> #2 [unw_get_proc_name() failed: -10] -> #3 i_panic[0x7fbaed2ee8ab] -> #4 [unw_get_proc_name() failed: -1] Mar 26 10:48:24 imap(alberto(a)bersol.info)<397><x8N6YuhNMs9YDtBg>: Fatal: master: service(imap): child 397 killed with signal 6 (core dumped) This breaks Dovecot and I have to restart the container, but it doesn't fix it either. When I access again, I've receive this errors again, until I disable sieve in the imap.conf: conf.d/20-imap.conf ------------------- ... protocol imap { # Space separated list of plugins to load (default is global mail_plugins). mail_plugins { # imap_sieve = yes imap_quota = yes last_login = yes } And I have to keep "imap_sieve" disabled. Regards, Alberto

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