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Date: Mon, 29 Jun 2015 11:24:04 +0200
From: Hanno Böck <>
Subject: Courier mail server: Write heap overflow in mailbot tool and out of
 bounds heap read in imap folder parser

Two memory access issues were found in the Courier mail server. These
issues were discovered by compiling the software with Address Sanitizer
(-fsanitize=address) and running the test suite.

In the file mailboxlist.c, part of the IMAP folder parser, there is a
memcmp call checking whether the fist six bytes of a string match
"SHARED". However the string can be less than six bytes, which will
cause an out of bounds read access. This issue is unlikely to cause
much trouble.

In the mailbot tool (mailbot.c) there is a memory allocation for a
zero-terminated list of pointers. The allocation only reserves one byte
for the zero termination, however it must be the size of the pointer (8
bytes on 64 bit systems). Therefore it causes a write heap overflow of
seven zero bytes. The code parses command line data, therefore it is
unlikely that any attacker controlled input is affected.

Both issues have been reported to Courier's developer Sam Varshavchik
on 27th June 2015 and were fixed with the release of courier 0.75 on
29th June 2015.

Commit / Patch (bundles some unrelated changes, the relevant parts are
in mailbot.c and mailboxlist.c)

Courier 0.75 release announcement

Hanno Böck


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