Bug 2305910 (CVE-2024-23185)

Summary: CVE-2024-23185 dovecot: very large headers can cause resource exhaustion when parsing message
Product: [Other] Security Response Reporter: Robb Gatica <rgatica>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedCC: redhat
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A security issue was found in Dovecot. Very large headers can lead to resource exhaustion when parsing messages. The message-parser normally reads reasonably sized chunks of the message. However, when it feeds them to the message-header-parser, it starts building up a "full_value" buffer out of the smaller chunks. The full_value buffer has no size limit so large headers can cause large memory usage. This issue occurs whether it is a single long header line or a single header split into multiple lines.
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Bug Depends On: 2305915, 2305914, 2305916, 2305917, 2305918    
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Description Robb Gatica 2024-08-19 20:47:40 UTC 
Vulnerability Details:
Very large headers can cause resource exhaustion when parsing message. The message-parser normally reads reasonably sized chunks of the message. However, when it feeds them to message-header-parser, it starts building up "full_value" buffer out of the smaller chunks. The full_value buffer has no size limit, so large headers can cause large memory usage. It doesn't matter whether it's a single long header line, or a single header split into multiple lines. This bug exists in all Dovecot versions.

Incoming mails typically have some size limits set by MTA, so even largest possible header size may still fit into Dovecot's vsz_limit. So attackers probably can't DoS a victim user this way. A user could APPEND larger mails though, allowing them to DoS themselves (although maybe cause some memory issues for the backend in general).

Workaround:
One can implement restrictions on headers on MTA component preceding Dovecot.

Fix:
Install non-vulnerable version of Dovecot. Patch can be found at https://github.com/dovecot/core/compare/f020e13%5E...ce88c33.patch
Comment 2 errata-xmlrpc 2024-09-09 01:29:09 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9.2 Extended Update Support

Via RHSA-2024:6465 https://access.redhat.com/errata/RHSA-2024:6465
Comment 3 errata-xmlrpc 2024-09-10 11:38:54 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9

Via RHSA-2024:6529 https://access.redhat.com/errata/RHSA-2024:6529
Comment 4 errata-xmlrpc 2024-09-24 02:48:45 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2024:6973 https://access.redhat.com/errata/RHSA-2024:6973