Infinite Loop in Pygments
An infinite loop in SMLLexer in Pygments versions 1.5 to 2.7.3 may lead to denial of service when performing syntax highlighting of a Standard ML (SML) source file, as demonstrated by input that only contains the "exception" keyword.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | pygments | >= 1.5, < 2.7.4 | 2.7.4 |
References
- https://bugzilla.redhat.com/show_bug.cgi?id=1922136
- https://www.debian.org/security/2021/dsa-4889
- https://lists.debian.org/debian-lts-announce/2021/05/msg00003.html
- https://lists.debian.org/debian-lts-announce/2021/05/msg00006.html
- https://github.com/advisories/GHSA-9w8r-397f-prfh
- https://nvd.nist.gov/vuln/detail/CVE-2021-20270
- https://github.com/pygments/pygments/commit/f91804ff4772e3ab41f46e28d370f57898700333
- https://github.com/pygments/pygments
- https://github.com/pypa/advisory-database/tree/main/vulns/pygments/PYSEC-2021-140.yaml
- https://www.oracle.com/security-alerts/cpuoct2021.html
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-835- Platform
- Python (PyPI)
- Package
pygments- Disclosed
- 23.03.2021
- Updated
- 11.10.2026 11:20
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2021-140 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-9w8r-397f-prfh - CC BY 4.0
Vulnerability history: pygments
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 5
- First → latest
- 01.2016 03.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 2
- Medium 1
- Low 1
Disclosures per year
- 2017: 0
- 2018: 0
- 2019: 0
- 2020: 0
- 2021: 2
- 2022: 0
- 2023: 1
- 2024: 0
- 2025: 0
- 2026: 1
earlier: 1
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Infinite Loop in Pygments this entry
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