CVE-2020-28024

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 4.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-05-06 · updated 2026-06-17
Weakness: CWE-787

Description

Exim 4 before 4.94.2 allows Buffer Underwrite that may result in unauthenticated remote attackers executing arbitrary commands, because smtp_ungetc was only intended to push back characters, but can actually push back non-character error codes such as EOF.

Affected products

Exim: from 4.00 before 4.94.2 — fixed in 4.94.2

How to fix

Upgrade to a fixed version: Exim 4.94.2. Check the vendor advisory for mitigations.

References

https://www.exim.org/static/doc/security/CVE-2020-qualys/CVE-2020-28024-UNGET.txt
https://www.exim.org/static/doc/security/CVE-2020-qualys/CVE-2020-28024-UNGET.txt

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