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Vulnerability record · CVE-2021-27291 · published 17 March 2021

CVE-2021-27291: Pygments inefficient regular expression (redos) vulnerability

Pygments · Pygments

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.

7.5 CVSS 3.1 High EPSS 3.9% · top 10.1% CWE-1333 · Inefficient regular expression (ReDoS)
7.5CVSS 3.1 base score, v2 5.0
3.9%EPSS exploitation probability, 30 days
NoNot in CISA KEV
3Affected product versions listed by NVD
18References, 2 tagged exploit
17 Jun 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

3 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://gist.github.com/b-c-ds/b1a2cc0c68a35c57188575eb496de5ce ExploitThird Party Advisory
https://github.com/pygments/pygments/commit/2e7e8c4a7b318f4032493773732754e418279a14 PatchThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/03/msg00024.html Mailing ListThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/05/msg00003.html Mailing ListThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/05/msg00006.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GSJRFHALQ7E3UV4FFMFU2YQ
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WSLD67LFGXOX2K5YNESSWAS
https://www.debian.org/security/2021/dsa-4878 Third Party Advisory
https://www.debian.org/security/2021/dsa-4889 Third Party Advisory
https://gist.github.com/b-c-ds/b1a2cc0c68a35c57188575eb496de5ce ExploitThird Party Advisory
https://github.com/pygments/pygments/commit/2e7e8c4a7b318f4032493773732754e418279a14 PatchThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/03/msg00024.html Mailing ListThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/05/msg00003.html Mailing ListThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/05/msg00006.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GSJRFHALQ7E3UV4FFMFU2YQ
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WSLD67LFGXOX2K5YNESSWAS
https://www.debian.org/security/2021/dsa-4878 Third Party Advisory
https://www.debian.org/security/2021/dsa-4889 Third Party Advisory

Track CVE-2021-27291 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

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Source: NIST National Vulnerability Database (record CVE-2021-27291), CISA KEV, FIRST EPSS (scores of 2026-09-29). This page is refreshed as NVD updates the record.