# CVE-2021-27291: Pygments vulnerable to Regular Expression Denial of Service (ReDoS)

Source: https://junglewise.ai/threats/cve-2021-27291-pygments-vulnerable-to-regular-expression-denial-of-service-redos  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2021-03-17  
License: CC BY 4.0 with a link back

CVE-2021-27291 · Severity: low · CVSS 3.1 · Published 2021-03-17

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.

Technologies: [pygments (PyPI)](https://junglewise.ai/threats/technologies/pygments). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2021-27291 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2021-27291 being exploited in the wild.

**How severe is CVE-2021-27291?** Low severity, with a CVSS score of 3.1, published 17 March 2021.

**Which products and versions are affected?** pygments (PyPI) ECOSYSTEM:introduced=1.1,fixed=2.7.4, GIT:introduced=0,fixed=2e7e8c4a7b318f4032493773732754e418279a14|ECOSYSTEM:introduced=1.1,fixed=2.7.4.

**Is there a fix for CVE-2021-27291?** Yes. pygments (PyPI): upgrade to 2.7.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2021-27291?** Check whether you run pygments (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- pygments (PyPI): upgrade to 2.7.4 or later

  ```sh
  pip install "pygments>=2.7.4"
  ```


## Affected products

- pygments (PyPI) ECOSYSTEM:introduced=1.1,fixed=2.7.4, GIT:introduced=0,fixed=2e7e8c4a7b318f4032493773732754e418279a14|ECOSYSTEM:introduced=1.1,fixed=2.7.4

## Identifiers

- CVE-2021-27291
- GHSA-pq64-v7f5-gqh8
- PYSEC-2021-141

## Related threats

- [PYSEC-2026-2987 - Pygments has Regular Expression Denial of Service (ReDoS) due to Inefficient Regex for GUID Matching](https://junglewise.ai/threats/cve-2026-4539-pygments-has-regular-expression-denial-of-service-redos-due-to)
- [PYSEC-2023-117 - A ReDoS issue was discovered in pygments/lexers/smithy.py in pygments through 2.15.0 via SmithyLexer.](https://junglewise.ai/threats/cve-2022-40896-pygments-vulnerable-to-redos)
- [Infinite Loop in Pygments](https://junglewise.ai/threats/cve-2021-20270-infinite-loop-in-pygments)
- [Command Injection in Pygments](https://junglewise.ai/threats/cve-2015-8557-command-injection-in-pygments)