CVE-2023-42821: The package `github.com/gomarkdown/markdown` is a Go library for parsing Markdown text and rendering as HTML

This week

HIGH 7.5REMOTEMITIGATE

CVE-2023-42821 is a high-severity flaw (CVSS 7.5) affecting markdown. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The package `github.com/gomarkdown/markdown` is a Go library for parsing Markdown text and rendering as HTML. Prior to pseudoversion `0.0.0-20230922105210-14b16010c2ee`, which corresponds with commit `14b16010c2ee7ff33a940a541d993bd043a88940`, parsing malformed markdown input with parser that uses parser.Mmark extension could result in out-of-bounds read vulnerability. To exploit the vulnerability, parser needs to have `parser.Mmark` extension se

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.3% (top 31%)
CISA exploited list	No
Weakness	CWE-125
Published	2023-09-22
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: gomarkdown

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

Am I affected?

Timeline

2023-09-22 17:15 UTCPublished CVE record published
2026-06-17 06:24 UTCUpdated Record last modified

gomarkdown markdown MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

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

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

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-2023-42821?

markdown: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2023-42821 being exploited?

CVE-2023-42821 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-2023-42821 affect?

CVE-2023-42821 affects markdown. Severity is high (CVSS 7.5). The package `github.com/gomarkdown/markdown` is a Go library for parsing Markdown text and rendering as HTML. Prior to pseudoversion `0.0.0-20230922105210-14b16010c2ee`, which corresponds with commit `14b16010c2ee7ff33a940a541d993bd043a8894

How urgent is CVE-2023-42821?

Priority 54/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

GitHub vulnerabilities

Related CVEs

CVE-2026-40890 HIGH 7.5 UPGRADE The package `github.com/gomarkdown/markdown` is a Go library for parsing Markdown text and rendering as HTML
CVE-2025-69534 HIGH 7.5 DOWNGRADE Python-Markdown version 3.8 contain a vulnerability where malformed HTML-like sequences can cause html.parser.
CVE-2018-1000874 MEDIUM 6.1 UPGRADE PHP cebe markdown parser version 1.2.0 and earlier contains a Cross Site Scripting (XSS) vulnerability in all

References

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