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HIGH

CVE-2021-27291

CVSS v3

7.5

HIGH

EPSS Score

3.9 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • pygmentsPyPIfrom 1.1 · fixed in 2.7.4
  • babelAlmaLinux:8all versions · fixed in 2.5.1-10.module_el8.6.0+2781+fed64c13and 1 other package
  • python-nose-docsAlmaLinux:8all versions · fixed in 1.3.7-31.module_el8.5.0+2569+5c5719bc
  • python-sqlalchemy-docAlmaLinux:8all versions · fixed in 1.3.2-2.module_el8.5.0+2569+5c5719bc
  • python-virtualenv-docAlmaLinux:8all versions · fixed in 15.1.0-21.module_el8.5.0+135+5ce32bc4
  • python2-attrsAlmaLinux:8all versions · fixed in 17.4.0-10.module_el8.6.0+2781+fed64c13
  • python2-backportsAlmaLinux:8all versions · fixed in 1.0-16.module_el8.6.0+2781+fed64c13
  • python2-backports-ssl_match_hostnameAlmaLinux:8all versions · fixed in 3.5.0.1-12.module_el8.6.0+2781+fed64c13

50 more package ranges on OSV.dev

Vendor advisories

  • CVE-2021-27291 Red Hat Product Security488 products fixed · 11 known affected

    python-pygments: ReDoS in multiple lexers

    python-pygments.src as a component of Red Hat Enterprise Linux 6 · python-pygments.src as a component of Red Hat Enterprise Linux 7 · resource-agents as a component of Red Hat Enterprise Linux 7

  • RHSA-2021:4150 Red Hat Product Security82 products fixed

    Red Hat Security Advisory: python36:3.6 security and bug fix update

  • RHSA-2021:4151 Red Hat Product Security264 products fixed

    Red Hat Security Advisory: python27:2.7 security update

  • RHSA-2021:4139 Red Hat Product Security36 products fixed

    Red Hat Security Advisory: resource-agents security, bug fix, and enhancement update

  • RHSA-2021:3252 Red Hat Product Security80 products fixed

    Red Hat Security Advisory: python27 security update

  • RHSA-2021:0781 Red Hat Product Security26 products fixed

    Red Hat Security Advisory: Red Hat Ansible Automation Platform 1.2.2 security and bug fix update

Full record on 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.

Technical details

Published
2021-03-17

Frequently asked questions

What is CVE-2021-27291?

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.

Is CVE-2021-27291 actively exploited?

Active exploitation of CVE-2021-27291 has not been confirmed. Its EPSS score was 3.9% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-27291?

CVE-2021-27291 has a CVSS v3 base score of 7.5 (HIGH severity).

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