How severe is CVE-2023-42821?

CVE-2023-42821 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2023-42821?

CVE-2023-42821 affects the following packages: github.com/gomarkdown/markdown (Go). Ecosystems affected: Go.

How do I fix CVE-2023-42821?

Update github.com/gomarkdown/markdown to 0.0.0-20230922105210-14b16010c2ee or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-42821 is resolved across your whole dependency graph.

How do I detect CVE-2023-42821 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/gomarkdown/markdown. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2023-42821 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2023-42821?

O3 pinpoints whether CVE-2023-42821 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2023-42821 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2023-42821, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2023-42821?

CVE-2023-42821 has an EPSS (Exploit Prediction Scoring System) score of 1.0%, placing it in the 60th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2023-42821?

CVE-2023-42821 is classified as Out-of-bounds Read (CWE-125). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2023-42821 published, and has it been updated?

CVE-2023-42821 was published on September 22, 2023 and was last updated on April 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

CVE-2023-42821

HIGH

github.com/gomarkdown/markdown Out-of-bounds Read while parsing citations

Also known asGHSA-m9xq-6h2j-65r2GO-2023-2074

Published

Sep 22, 2023

Updated

Apr 10, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

EPSS Exploitation Probability

via FIRST.org ↗

1.0%probability of exploitation in next 30 days

Lower Risk60th percentile+0.56%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

1 pkg affected

🐹github.com/gomarkdown/markdown

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

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 set. The panic occurs inside the citation.go file on the line 69 when the parser tries to access the element past its length. This can result in a denial of service. Commit 14b16010c2ee7ff33a940a541d993bd043a88940/pseudoversion 0.0.0-20230922105210-14b16010c2ee contains a patch for this issue.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/gomarkdown/markdown`	all versions	0.0.0-20230922105210-14b16010c2ee

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

The package `github.com/gomarkdown/markdown` is a Go library for parsing…

github.comNVDSep 2023

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/gomarkdown/markdown. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/gomarkdown/markdown to 0.0.0-20230922105210-14b16010c2ee or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-42821 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2023-42821 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2023-42821. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

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 set. The panic occurs inside the `citation.go` file on the line 69 when the parser tries to access the element past its length. This can result in a den

O3 Security · Impact-Aware SCA

Is CVE-2023-42821 in your dependencies?

O3 detects CVE-2023-42821 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works