CVE-2021-27291

26

FAUCET Score

CVE-2021-27291 is a Regular Expression Denial of Service (ReDoS) vulnerability affecting Pygments versions 1.1 and above, fixed in 2.7.4, as well as various Debian and Fedora distributions. Attackers can craft malicious input to exploit inefficient regular expressions within Pygments' language lexers, leading to a denial of service due to exponential or cubic worst-case complexity. Rated 7.5 HIGH on CVSS, this vulnerability requires no user interaction or privileges and can be exploited remotely. There is currently no evidence of active exploitation, public exploit code, or significant community discussion surrounding this CVE.

Impacted Technologies

Vendor	Product	Version(s)	CPE
		>= 1.1, < 2.7.4CPE matchmatch criteria	cpe:2.3:a:pygments:pygments::::::::
		9.0CPE matchmatch criteria	cpe:2.3:o:debian:debian_linux:9.0:::::::*
		10.0CPE matchmatch criteria	cpe:2.3:o:debian:debian_linux:10.0:::::::*
		32CPE matchmatch criteria	cpe:2.3:o:fedoraproject:fedora:32:::::::*
		33CPE matchmatch criteria	cpe:2.3:o:fedoraproject:fedora:33:::::::*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

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

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

HIGH

Exploitability Score

3.9

Impact Score

3.6

CvssVersion

3.1

Exploit Intelligence

EPSS Score

3.91%

Probability of exploitation in next 30 days

EPSS Percentile

89.2%

Percentile rank of EPSS score among Peer Group

As of 2026-07-27

Model: v2026.06.15

This CVE's current EPSS score of 0.0391 is in the 81st percentile among its peer group of 51,506 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (37)

github_advisorypatch availablevia nvd_reference

microsoftpatch availablevia msrc

Product: 16993-17084Fixed in: 2.7.4-1

microsoftpatch availablevia msrc

Product: 19947-17084Fixed in: 2.7.4-1

microsoftpatch availablevia msrc

Product: Azure Linux 3.0 ARMFixed in: 2.7.4-1

microsoftpatch availablevia msrc

Product: azl3 python-pygments 2.7.4-1 on Azure Linux 3.0Fixed in: 2.7.4-1

microsoftpatch availablevia msrc

Product: azl3 python-pygments 2.5.2-1 on Azure Linux 3.0Fixed in: 2.7.4-1

microsoftpatch availablevia msrc

Product: CBL Mariner 1.0 x64Fixed in: 2.4.2-6

microsoftpatch availablevia msrc

Product: CBL Mariner 1.0 ARMFixed in: 2.4.2-6

microsoftpatch availablevia msrc

Product: CBL Mariner 2.0 x64Fixed in: 2.4.2-7

microsoftpatch availablevia msrc

Product: CBL Mariner 2.0 ARMFixed in: 2.4.2-7

microsoftpatch availablevia msrc

Product: Azure Linux 3.0 x64Fixed in: 2.7.4-1

pippatch availablevia ghsa

Product: PygmentsFixed in: 2.7.4

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: python3-django-0:2.2.18-1.el8pc

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: python-bleach-0:3.3.0-1.el8pc

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: python-bleach-allowlist-0:1.0.3-1.el8pc

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: python-galaxy-importer-0:0.2.15-1.el8pc

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: python-galaxy-ng-0:4.2.2-1.el8pc

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: python-pulp-ansible-1:0.5.6-1.el8pc

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 8Fixed in: python36:3.6-8050020210811103506.982725ab

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 8Fixed in: python27:2.7-8050020210811095446.3e7ace8b

redhatpatch availablevia redhat_api

Product: Red Hat Enterprise Linux 8Fixed in: resource-agents-0:4.1.1-98.el8

redhatpatch availablevia redhat_api

Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: python27-babel-0:0.9.6-10.el7

redhatpatch availablevia redhat_api

Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: python27-python-0:2.7.18-3.el7

redhatpatch availablevia redhat_api

Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: python27-python-jinja2-0:2.6-16.el7

redhatpatch availablevia redhat_api

Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: python27-python-pygments-0:1.5-5.el7

redhatpatch availablevia redhat_api

Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.7 EUSFixed in: python27-babel-0:0.9.6-10.el7

redhatpatch availablevia redhat_api

Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.7 EUSFixed in: python27-python-0:2.7.18-3.el7

redhatpatch availablevia redhat_api

Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.7 EUSFixed in: python27-python-jinja2-0:2.6-16.el7

redhatpatch availablevia redhat_api

Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.7 EUSFixed in: python27-python-pygments-0:1.5-5.el7

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: automation-hub-0:4.2.2-1.el7pc

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python3-django-0:2.2.18-1.el7pc

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python-bleach-0:3.3.0-1.el7pc

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python-bleach-allowlist-0:1.0.3-1.el7pc

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python-galaxy-importer-0:0.2.15-1.el7pc

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python-galaxy-ng-0:4.2.2-1.el7pc

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: automation-hub-0:4.2.2-1.el8pc

redhatpatch availablevia redhat_api

Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python-pulp-ansible-1:0.5.6-1.el7pc

Vendor Advisories (4)

microsoft2024-Sep/CVE-2021-27291

CVE-2021-27291

pipGHSA-pq64-v7f5-gqh8high

Pygments vulnerable to Regular Expression Denial of Service (ReDoS)

microsoft2021-Mar/CVE-2021-27291Important

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.

redhatCVE-2021-27291Moderate

python-pygments: ReDoS in multiple lexers

References

gist.github.com / b-c-ds/b1a2cc0c68a35c57188575eb496de5ce

ExploitThird Party Advisory

github.com / pygments/pygments/commit/2e7e8c4a7b318f4032493773732754e418279a14

PatchThird Party Advisory

lists.debian.org / debian-lts-announce/2021/03/msg00024.html

Mailing ListThird Party Advisory

lists.debian.org / debian-lts-announce/2021/05/msg00003.html

Mailing ListThird Party Advisory

lists.debian.org / debian-lts-announce/2021/05/msg00006.html

Mailing ListThird Party Advisory

lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/GSJRFHALQ7E3UV4FFMFU2YQ6LUDHAI55

lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/WSLD67LFGXOX2K5YNESSWAS4AGZIJTUQ

debian.org / security/2021/dsa-4878

Third Party Advisory

debian.org / security/2021/dsa-4889

Third Party Advisory