#VU20432 Out-of-bounds write in Dovecot - CVE-2019-11500

Vulnerability identifier: #VU20432

Vulnerability risk: High

CVSSv4.0: 8.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P/U:Amber]

CVE-ID: CVE-2019-11500

CWE-ID: CWE-787

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Dovecot
Server applications / Mail servers

Vendor: Dovecot

Description

The vulnerability allows a remote attacker to compromise vulnerable system.

The vulnerability exists due to a boundary error within IMAP and ManageSieve protocol implementation the when scanning data in quoted strings. A remote attacker can send a specially crafted request to the affected server, trigger out-of-bounds write and execute arbitrary code on the target system.

Exploitation example:

perl -e 'print "a id (\"foo\" \"".("x"x1021)."\\A\" \"bar\"
\"\000".("x"x1020)."\\A\")\n"' | nc localhost 143

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Dovecot: 2.2.0 - 2.3.7.1

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External links
https://dovecot.org/pipermail/dovecot-news/2019-August/000418.html
https://github.com/dovecot/core/commit/85fcb895ca7f0bcb8ee72047fe0e1e78532ff90b
https://github.com/dovecot/core/commit/f904cbdfec25582bc5e2a7435bf82ff769f2526a
https://github.com/dovecot/pigeonhole/commit/7ce9990a5e6ba59e89b7fe1c07f574279aed922c
https://github.com/dovecot/pigeonhole/commit/4a299840cdb51f61f8d1ebc0210b19c40dfbc1cc

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, proof of concept for this vulnerability is available.