CVE-2020-5238: The table extension in GitHub Flavored Markdown before version 0.29.0.gfm.1 takes O(n * n) time to parse certa

Q: How do I fix CVE-2020-5238?

github flavored markdown: upgrade to 0.29.0.gfm.1; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2020-5238 being exploited?

CVE-2020-5238 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2020-5238 affect?

CVE-2020-5238 affects github flavored markdown, fedora. Severity is medium (CVSS 6.5). 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 ser

Q: How urgent is CVE-2020-5238?

Priority 42/100. No elevated risk signals yet.

This month

MEDIUM 6.5UPGRADEMITIGATE

CVE-2020-5238 is a medium-severity flaw (CVSS 6.5) affecting github flavored markdown, fedora. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	1.6% (top 25%)
CISA exploited list	No
Weakness	CWE-20
Published	2020-07-01
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: fedoraproject · github flavored markdown project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2020-07-01 23:15 UTCPublished CVE record published
2026-06-17 03:21 UTCUpdated Record last modified

github flavored markdown project github flavored markdown UPGRADE

Affected: < 0.29.0.gfm.1

Fixed in: 0.29.0.gfm.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy github-flavored-markdown || rpm -q github-flavored-markdown || github-flavored-markdown --version

2. UPGRADE to 0.29.0.gfm.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade github-flavored-markdown

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade github-flavored-markdown

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

fedoraproject fedora MITIGATE

Affected: 31 · 32 · 33

Fixed in: no fixed release known

Safe to downgrade to: a release before 31

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2020-5238?

github flavored markdown: upgrade to 0.29.0.gfm.1; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-5238 being exploited?

CVE-2020-5238 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2020-5238 affect?

CVE-2020-5238 affects github flavored markdown, fedora. Severity is medium (CVSS 6.5). 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 ser

How urgent is CVE-2020-5238?

Priority 42/100. No elevated risk signals yet.

Software pages

GitHub vulnerabilities

References

← Back to latest CVEs