What’s Vulnerable › Vulnerabilities

CVE-2020-5238: Denial of service in table parsing in cmark-gfm

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-07-01 · updated 2026-06-17
• Weakness: CWE-20

Description

The table extension in GitHub Flavored Markdown before version 0.29.0.gfm.1 takes O(n * n) time to parse certain inputs. An attacker could craft a markdown table which would take an unreasonably long time to process, causing a denial of service. This issue does not affect the upstream cmark project. The issue has been fixed in version 0.29.0.gfm.1.

Affected products

• Fedoraproject Fedora: 31, 32, 33
• Github Flavored Markdown Project Github Flavored Markdown: before 0.29.0.gfm.1 — fixed in 0.29.0.gfm.1

How to fix

Upgrade to a fixed version: Github Flavored Markdown Project Github Flavored Markdown 0.29.0.gfm.1. Check the vendor advisory for mitigations.

References

• https://github.com/github/cmark-gfm/commit/85d895289c5ab67f988ca659493a64abb5fec7b4
• https://github.com/github/cmark-gfm/security/advisories/GHSA-7gc6-9qr5-hc85
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TCDHBTUFIOYRIS5HAS6PZNBNMB7IOAX3/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WMQFOQQCWOAMQ4I2XIVCVOXXIJ75HDCW/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZGJH2A4VAV54X6NSCNNGSEIGIIY5N2VR/
• https://github.com/github/cmark-gfm/commit/85d895289c5ab67f988ca659493a64abb5fec7b4
• https://github.com/github/cmark-gfm/security/advisories/GHSA-7gc6-9qr5-hc85
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TCDHBTUFIOYRIS5HAS6PZNBNMB7IOAX3/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WMQFOQQCWOAMQ4I2XIVCVOXXIJ75HDCW/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZGJH2A4VAV54X6NSCNNGSEIGIIY5N2VR/

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