CVE-2021-20270: Debian Linux

High severity, CVSS 7.5. EPSS: 2.8% chance of exploitation in the next 30 days.

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 products

• Debian Debian Linux: version 9.0 only; version 10.0 only
• Fedoraproject Fedora: version 33 only
• Pygments Pygments: from 1.5, up to and including 2.7.3
• Red Hat Enterprise Linux: version 7.0 only; version 8.0 only
• Red Hat Openshift Container Platform: version 3.11 only; version 4.0 only
• Red Hat Openstack Platform: version 10.0 only
• Red Hat Software Collections: affected versions not specified

Published 2021-03-23. Last modified 2026-06-17.