SPA authentication bypass in Exim

1) Out-of-bounds read

EUVDB-ID: #VU27959

Risk: Medium

CVSSv3.1: 4.9 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:U/RL:U/RC:C]

CVE-ID: CVE-2020-12783

CWE-ID: CWE-125 - Out-of-bounds read

Exploit availability: No

Description

The vulnerability allows a remote attacker to gain access to potentially sensitive information.

The vulnerability exists due to a boundary condition in the SPA authenticator within auths/spa.c and auths/auth-spa.c. A remote attacker can bypass SPA/NTLM authentication.

Mitigation

Install update from vendor's website.

Vulnerable software versions

Exim: 4.00 - 4.93.0.4

External links

http://bugs.exim.org/show_bug.cgi?id=2571
http://git.exim.org/exim.git/commit/57aa14b216432be381b6295c312065b2fd034f86
http://git.exim.org/exim.git/commit/a04174dc2a84ae1008c23b6a7109e7fa3fb7b8b0
http://www.debian.org/security/2020/dsa-4687

Q & A

Can this vulnerability be exploited remotely?

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

How the attacker can exploit this vulnerability?

The attacker would have to send a specially crafted request to the affected application in order to exploit this vulnerability.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.