Amazon Linux AMI update for exim

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

EUVDB-ID: #VU73857

Risk: Medium

CVSSv3.1: 6.3 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N/E:U/RL:O/RC:C]

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 packages:

i686:
    exim-debuginfo-4.92-1.36.amzn1.i686
    exim-mysql-4.92-1.36.amzn1.i686
    exim-mon-4.92-1.36.amzn1.i686
    exim-greylist-4.92-1.36.amzn1.i686
    exim-4.92-1.36.amzn1.i686
    exim-pgsql-4.92-1.36.amzn1.i686

src:
    exim-4.92-1.36.amzn1.src

x86_64:
    exim-greylist-4.92-1.36.amzn1.x86_64
    exim-mysql-4.92-1.36.amzn1.x86_64
    exim-mon-4.92-1.36.amzn1.x86_64
    exim-pgsql-4.92-1.36.amzn1.x86_64
    exim-4.92-1.36.amzn1.x86_64
    exim-debuginfo-4.92-1.36.amzn1.x86_64

Vulnerable software versions

Amazon Linux AMI: All versions

exim: before 4.92-1.36

External links

http://alas.aws.amazon.com/ALAS-2023-1722.html

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.