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Fencer Vulns
high 7.5

CVE-2021-27291 json

Pygments vulnerable to Regular Expression Denial of Service (ReDoS)

published 2021-03-17 5 y ago modified 2026-06-17 4 mo ago also GHSA-pq64-v7f5-gqh8 , PYSEC-2021-141 , EUVD-2021-0208

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
3.9%
EPSS 3.9% chance of exploitation in 30 days, percentile 90%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi pygments 2.7.4
  • pygments pygments 2.7.4
  • pygments Debian 14, Debian 13, Debian 12 2.7.1+dfsg-2.1
  • mediawiki Debian 14, Debian 13, Debian 12 1:1.35.2-1

debian advisories DEBIAN-CVE-2021-27291

  • pygments Ubuntu 16.04 LTS 2.1+dfsg-1ubuntu0.2
  • pygments Ubuntu 18.04 LTS 2.2.0+dfsg-1ubuntu0.2
  • pygments Ubuntu 20.04 LTS 2.3.1+dfsg-1ubuntu2.2
  • pygments Ubuntu Pro 14.04 LTS 1.6+dfsg-1ubuntu1.1+esm1

ubuntu advisories UBUNTU-CVE-2021-27291

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • pytz RHEL 8 2017.2-12.module+el8.1.0+3111+de3f2d8e
  • babel RHEL 8 2.5.1-10.module+el8.5.0+11014+88fc0d0b
  • numpy RHEL 8 1:1.14.2-16.module+el8.4.0+9406+221a4565
  • scipy RHEL 8 1.0.0-21.module+el8.5.0+10858+05337455
  • Cython RHEL 8 0.28.1-7.module+el8.1.0+3111+de3f2d8e
  • pytest RHEL 8 3.4.2-13.module+el8.1.0+3111+de3f2d8e
  • PyYAML RHEL 8 3.12-16.module+el8.1.0+3111+de3f2d8e
  • python2 RHEL 8 2.7.18-7.module+el8.5.0+12203+77770ab7

red hat advisories RHSA-2021:4151RHSA-2021:3252RHSA-2021:0781RHSA-2021:4139RHSA-2021:4150

  • python-Pygments SLES for SAP 15, SLES 15-LTSS, SLE Module for Package Hub 15 SP3 +3 more 2.2.0-4.9.1
  • python-Pygments SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +4 more 2.6.1-7.10.1
  • python-Pygments SLE Module for Basesystem 15 SP3 2.6.1-4.3.1
  • python-Pygments SLE Module for Public Cloud 12 2.4.2-10.7.1

suse advisories SUSE-SU-2021:3841-1SUSE-SU-2021:3840-1SUSE-SU-2021:3839-1SUSE-SU-2021:3814-1

  • python-Pygments openSUSE Leap 15.2 2.6.1-lp152.5.12.1
  • python-Pygments openSUSE Leap 15.3 2.2.0-4.9.1
  • python-Pygments openSUSE Leap 15.3 2.6.1-4.3.1

opensuse advisories openSUSE-SU-2021:1521-1openSUSE-SU-2021:3841-1openSUSE-SU-2021:3839-1

  • babel AlmaLinux 8 2.5.1-10.module_el8.6.0+2781+fed64c13
  • python2-py AlmaLinux 8 1.5.3-6.module_el8.6.0+2781+fed64c13
  • python2-dns AlmaLinux 8 1.15.0-10.module_el8.6.0+2781+fed64c13
  • python2-six AlmaLinux 8 1.11.0-6.module_el8.6.0+2781+fed64c13
  • python2-bson AlmaLinux 8 3.7.0-1.module_el8.6.0+2781+fed64c13
  • python2-idna AlmaLinux 8 2.5-7.module_el8.6.0+2781+fed64c13
  • python2-mock AlmaLinux 8 2.0.0-13.module_el8.6.0+2781+fed64c13
  • python2-nose AlmaLinux 8 1.3.7-31.module_el8.6.0+2781+fed64c13

almalinux advisories ALSA-2021:4151ALSA-2021:4150ALSA-2021:4139

  • pytz Rocky Linux 8 2017.2-12.module+el8.5.0+706+735ec4b3
  • pytz Rocky Linux 8 2017.2-12.module+el8.4.0+403+9ae17a31
  • babel Rocky Linux 8 2.5.1-10.module+el8.5.0+706+735ec4b3
  • numpy Rocky Linux 8 1:1.14.2-16.module+el8.5.0+706+735ec4b3
  • numpy Rocky Linux 8 1:1.14.2-16.module+el8.4.0+403+9ae17a31
  • scipy Rocky Linux 8 1.0.0-21.module+el8.5.0+671+195e4563
  • Cython Rocky Linux 8 0.28.1-7.module+el8.5.0+706+735ec4b3
  • Cython Rocky Linux 8 0.28.1-7.module+el8.4.0+403+9ae17a31

rocky linux advisories RLSA-2021:4151RLSA-2021:4150RLSA-2021:4139

  • py3-pygments Alpine 3.11 2.5.2-r1
  • py3-pygments Alpine 3.12 2.6.1-r1

alpine advisories ALPINE-CVE-2021-27291

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • python-pygments Azure Linux 3.0 2.7.4-1
  • python-pygments CBL-Mariner 2.0 2.4.2-7

azure linux advisories AZL-35138AZL-6812

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

  • python-pygments Arch Linux 2.7.4-1
  • mediawiki Arch Linux 1.35.2-1

arch linux advisories AVG-1662AVG-1775

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-27291 updated cvss 7.5

python-pygments: ReDoS in multiple lexers

  • Red Hat Enterprise Linux 6 python-pygments Red Hat Enterprise Linux 7 python-pygments, resource-agents, resource-agents-gcp, resource-agents-sap, sap-cluster-connector, resource-agents-aliyun, +2 more Red Hat OpenStack Platform 10 (Newton) python-pygments
    affected: no fix planned “Out of support scope”
  • Red Hat Automation Hub 4.2 for RHEL 7 python-bleach 3.3.0-1.el7pc, automation-hub 4.2.2-1.el7pc, python3-bleach 3.3.0-1.el7pc, python3-django 2.2.18-1.el7pc, python-galaxy-ng 4.2.2-1.el7pc, python3-galaxy-ng 4.2.2-1.el7pc, +6 more Red Hat Automation Hub 4.2 for RHEL 8 python-bleach 3.3.0-1.el8pc, automation-hub 4.2.2-1.el8pc, python3-bleach 3.3.0-1.el8pc, python3-django 2.2.18-1.el8pc, python-galaxy-ng 4.2.2-1.el8pc, python3-galaxy-ng 4.2.2-1.el8pc, +6 more
    fixed: vendor fix RHSA-2021:0781
  • Red Hat Enterprise Linux AppStream (v. 8) pytz 2017.2-12.module+el8.1.0+3111+de3f2d8e, PyYAML 3.12-16.module+el8.1.0+3111+de3f2d8e, babel 2.5.1-10.module+el8.5.0+11014+88fc0d0b, Cython 0.28.1-7.module+el8.1.0+3111+de3f2d8e, numpy 1.14.2-16.module+el8.4.0+9406+221a4565, pytest 3.4.2-13.module+el8.1.0+3111+de3f2d8e, +108 more
    fixed: vendor fix RHSA-2021:4151
  • Red Hat Enterprise Linux High Availability (v. 8) resource-agents 4.1.1-98.el8, resource-agents-gcp 4.1.1-98.el8, resource-agents-paf 4.1.1-98.el8, resource-agents-aliyun 4.1.1-98.el8 Red Hat Enterprise Linux Resilient Storage (v. 8) resource-agents 4.1.1-98.el8, resource-agents-gcp 4.1.1-98.el8, resource-agents-paf 4.1.1-98.el8, resource-agents-aliyun 4.1.1-98.el8
    fixed: vendor fix RHSA-2021:4139
  • Red Hat Software Collections for Red Hat Enterprise Linux Server (v. 7) python27-babel 0.9.6-10.el7, python27-python 2.7.18-3.el7, python27-tkinter 2.7.18-3.el7, python27-python-jinja2 2.6-16.el7, python27-python-libs 2.7.18-3.el7, python27-python-test 2.7.18-3.el7, +3 more Red Hat Software Collections for Red Hat Enterprise Linux Server EUS (v. 7.7) python27-babel 0.9.6-10.el7, python27-python 2.7.18-3.el7, python27-tkinter 2.7.18-3.el7, python27-python-jinja2 2.6-16.el7, python27-python-libs 2.7.18-3.el7, python27-python-test 2.7.18-3.el7, +3 more Red Hat Software Collections for Red Hat Enterprise Linux Workstation (v. 7) python27-babel 0.9.6-10.el7, python27-python 2.7.18-3.el7, python27-tkinter 2.7.18-3.el7, python27-python-jinja2 2.6-16.el7, python27-python-libs 2.7.18-3.el7, python27-python-test 2.7.18-3.el7, +3 more
    fixed: vendor fix RHSA-2021:3252

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

3.91% chance of exploitation in the next 30 days, higher than 90% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • gist.github.com https://gist.github.com/b-c-ds/b1a2cc0c68a35c57188575eb496de5ce referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
pypi pygments
>=1.1, <2.7.4
2.7.4

Classification

Weakness
  • CWE-1333 Inefficient Regular Expression Complexity
  • CWE-400 Uncontrolled Resource Consumption

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.