What’s Vulnerable › Vulnerabilities

CVE-2021-27291

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 3.9% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-03-17 · updated 2026-06-17
• Weakness: CWE-1333

Description

In pygments 1.1+, fixed in 2.7.4, the lexers used to parse programming languages rely heavily on regular expressions. Some of the regular expressions have exponential or cubic worst-case complexity and are vulnerable to ReDoS. By crafting malicious input, an attacker can cause a denial of service.

Affected products

• Debian Linux: 9.0, 10.0
• Fedoraproject Fedora: 32, 33
• Pygments: from 1.1 before 2.7.4 — fixed in 2.7.4

How to fix

Upgrade to a fixed version: Pygments 2.7.4. Check the vendor advisory for mitigations.

References

• https://gist.github.com/b-c-ds/b1a2cc0c68a35c57188575eb496de5ce
• https://github.com/pygments/pygments/commit/2e7e8c4a7b318f4032493773732754e418279a14
• https://lists.debian.org/debian-lts-announce/2021/03/msg00024.html
• https://lists.debian.org/debian-lts-announce/2021/05/msg00003.html
• https://lists.debian.org/debian-lts-announce/2021/05/msg00006.html
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GSJRFHALQ7E3UV4FFMFU2YQ6LUDHAI55/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WSLD67LFGXOX2K5YNESSWAS4AGZIJTUQ/
• https://www.debian.org/security/2021/dsa-4878
• https://www.debian.org/security/2021/dsa-4889
• https://gist.github.com/b-c-ds/b1a2cc0c68a35c57188575eb496de5ce
• https://github.com/pygments/pygments/commit/2e7e8c4a7b318f4032493773732754e418279a14
• https://lists.debian.org/debian-lts-announce/2021/03/msg00024.html

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