CVE-2026-40890 github.com/gomarkdown/markdown: Out-of-bounds Read in SmartypantsRenderer
A malformed Markdown input can cause an out-of-bounds read or panic in the SmartypantsRenderer, leading to a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-40890?
CVE-2026-40890 is a high-severity denial of service vulnerability in gomarkdown markdown, published on 21 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
The package `github.com/gomarkdown/markdown` is a Go library for parsing Markdown text and rendering as HTML. Processing a malformed input containing a < character that is not followed by a > character anywhere in the remaining text with a SmartypantsRenderer will lead to Out of Bounds read or a panic. This vulnerability is fixed with commit 759bbc3e32073c3bc4e25969c132fc520eda2778.
Weakness: CWE-125
Which versions are affected by CVE-2026-40890?
3 open source packages ship an affected version, including github.com/gomarkdown/markdown. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/gomarkdown/markdown Go | All versions | 0.0.0-20260411013819-759bbc3e3207 |
github.com/gomarkdown/markdown Go | All versions | 0.0.0-20260411013819-759bbc3e3207 |
github.com/gomarkdown/markdown Go | All versions | 0.0.0-20260411013819-759bbc3e3207 |
Products include Gomarkdown Markdown.
How do I fix CVE-2026-40890?
Upgrade github.com/gomarkdown/markdown to 0.0.0-20260411013819-759bbc3e3207 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-40890 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40890 exists.
Other vulnerabilities in gomarkdown markdown
Sources
Also known as CLEANSTART-2026-FB77791, CLEANSTART-2026-GL95997, DEBIAN-CVE-2026-40890, GHSA-77fj-vx54-gvh7, GO-2026-5208, MINI-6mmg-2qhp-9px8 and 6 more.