Integer underflow in Exim - CVE-2020-28024

Vulnerability identifier: #VU52870

CSH Severity: High

CVSS v4: 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]

CVE-ID: CVE-2020-28024

CWE-ID: CWE-191

Exploitation vector: Remote access

Exploit availability: No public exploit available

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

The vulnerability exists due to integer underflow in smtp_ungetc() function. A remote attacker can send a specially crafted data to the application, trigger integer underflow and execute arbitrary code on the target system.

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

Exim
Amazon Linux AMI
Gentoo Linux
Ubuntu
exim4 (Debian package)
exim4-daemon-light (Ubuntu package)
exim4-daemon-heavy (Ubuntu package)
exim4-base (Ubuntu package)
exim

Install updates from vendor's website.

Exim - update to 4.94.2
exim4 (Debian package) - update to 4.92-8+deb10u6
exim4-daemon-light (Ubuntu package) - addressed in versions 4.86.22ubuntu2.6+esm1, 4.90.1-1ubuntu1.8, 4.93-13ubuntu1.5, 4.94-7ubuntu1.2, 4.94-15ubuntu1.2
exim4-daemon-heavy (Ubuntu package) - addressed in versions 4.86.22ubuntu2.6+esm1, 4.90.1-1ubuntu1.8, 4.93-13ubuntu1.5, 4.94-7ubuntu1.2, 4.94-15ubuntu1.2
exim4-base (Ubuntu package) - addressed in versions 4.86.22ubuntu2.6+esm1, 4.90.1-1ubuntu1.8, 4.93-13ubuntu1.5, 4.94-7ubuntu1.2, 4.94-15ubuntu1.2
exim - update to 4.92-1.33

• http://seclists.org/oss-sec/2021/q2/91

• Multiple vulnerabilities in Exim
• Gentoo update for Exim
• Debian update for exim4
• Ubuntu update for exim4
• Ubuntu update for exim4
• Amazon Linux AMI update for exim