Can dovecot be leveraged to exploit Solr/Log4shell?

Scott qmail at
Tue Dec 14 02:23:56 UTC 2021

Is this assuming you log at some verbose level ? What if you log at WARN or higher ? 

For production it seems kind of silly to log search queries anyways.


-----Original Message-----
From: dovecot <dovecot-bounces at> On Behalf Of John Fawcett
Sent: Monday, December 13, 2021 8:52 PM
To: dovecot at
Subject: Re: Can dovecot be leveraged to exploit Solr/Log4shell?

On 13/12/2021 23:43, Joseph Tam wrote:
> I'm surprised I haven't seen this mentioned yet.
> An internet red alert went out Friday on a new zero-day exploit. It is 
> an input validation problem where Java's Log4j module can be 
> instructed via a specially crafted string to fetch and execute code 
> from a remote LDAP server.  It has been designated the Log4shell exploit (CVE-2021-44228).
> Although I don't use it, I immediately thought of Solr, which provides 
> some dovecot installations with search indexing.  Can dovecot be made 
> to pass on arbitrary loggable strings to affected versions of Solr 
> (7.4.0-7.7.3, 8.0.0-8.11.0)?
> Those running Solr to implement Dovecot FTS should look at
> og4j-cve-2021-44228
> Joseph Tam <jtam.home at>

Solr logs the search strings passed, so potentially authenticated users could log malicious strings by searching for them. I do see escaping of some special characters in the log, but not sure if that would be a sufficient mitigation. In my web server logs I see all kinds of patterns that are trying to circumvent WAF rules, so maybe someone will come up with a way of getting the malicious string into the solr log.

As Apache Solr is mentioned as one of the software that is impacted, the mitigations are to upgrade to a non vulnerable version asap and in the meantime turn off JNDI lookups.


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