#VU21399 Heap-based buffer overflow in Exim - CVE-2019-16928

Vulnerability identifier: #VU21399

Vulnerability risk: High

CVSSv4.0: 9.3 [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:A/U:Amber]

CVE-ID: CVE-2019-16928

CWE-ID: CWE-122

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Exim
Server applications / Mail servers

Vendor: Exim

Description

The vulnerability allows a remote attacker to execute arbitrary code on the target system.

The vulnerability exists due to a boundary error within the string_vformat() function in string.c when processing an overly long argument for EHLO command. A remote non-authenticated attacker can send a very long string as an argument for the EHLO command, trigger a heap-based buffer overflow and execute arbitrary code on the target system.

Successful exploitation of this vulnerability may result in complete compromise of vulnerable system.

Mitigation
Install the latest version from vendor's website.

Vulnerable software versions

Exim: 4.92 - 4.92.2

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External links
http://www.openwall.com/lists/oss-security/2019/09/28/1
http://www.openwall.com/lists/oss-security/2019/09/28/2
http://www.openwall.com/lists/oss-security/2019/09/28/3
http://bugs.exim.org/show_bug.cgi?id=2449
http://git.exim.org/exim.git/commit/478effbfd9c3cc5a627fc671d4bf94d13670d65f
http://lists.exim.org/lurker/message/20190927.032457.c1044d4c.en.html

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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?

Yes. This vulnerability is being exploited in the wild.