Ubuntu update for exim4

1) Man-in-the-Middle (MitM) attack

EUVDB-ID: #VU73857

Risk: Medium

CVSSv4.0: 2.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2021-38371

CWE-ID: CWE-300 - Channel Accessible by Non-Endpoint ('Man-in-the-Middle')

Exploit availability: No

Description

The vulnerability allows a remote attacker to perform MitM attack.

The vulnerability exists due to the way Exim handles concurrent STARTTLS sessions when sending out emails. A malicious server can send a response to the *next* command within the existing STARTTLS sessions and force the Exim to treat this session as trusted.

Mitigation

Update the affected package exim4 to the latest version.

Vulnerable software versions

Ubuntu: 14.04 - 20.04

eximon4 (Ubuntu package): before Ubuntu Pro

exim4-base (Ubuntu package): before Ubuntu Pro

exim4 (Ubuntu package): before Ubuntu Pro

CPE2.3

• cpe:2.3:o:canonical:ubuntu:14.04:*:*:*:*:*:*:*
• cpe:2.3:o:canonical:ubuntu:16.04:*:*:*:*:*:*:*
• cpe:2.3:o:canonical:ubuntu:18.04:*:*:*:*:*:*:*
• cpe:2.3:o:canonical:ubuntu:20.04:*:*:*:*:*:*:*
• cpe:2.3:a:canonical:eximon4_ubuntu_package:*:*:*:*:*:ubuntu:*:*
• cpe:2.3:a:canonical:exim4-base_ubuntu_package:*:*:*:*:*:ubuntu:*:*
• cpe:2.3:a:canonical:exim4_ubuntu_package:*:*:*:*:*:ubuntu:*:*

External links

https://ubuntu.com/security/notices/USN-6881-1

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.