# CVE-2026-40890: Go Markdown has an Out-of-bounds Read in SmartypantsRenderer

Source: https://junglewise.ai/threats/cve-2026-40890-go-markdown-has-an-out-of-bounds-read-in-smartypantsrenderer  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-21. Updated: 2026-05-11  
License: CC BY 4.0 with a link back

CVE-2026-40890 · Severity: high · CVSS 7.5 · Published 2026-04-21

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.

Technologies: [github.com/gomarkdown/markdown (Go)](https://junglewise.ai/threats/technologies/github-com-gomarkdown-markdown). Vendors: [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-40890 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-40890 being exploited in the wild.

**How severe is CVE-2026-40890?** High severity, with a CVSS score of 7.5, published 21 April 2026.

**Which products and versions are affected?** github.com/gomarkdown/markdown (Go) < 0.0.0-20260411013819-759bbc3e3207, SEMVER:introduced=0,fixed=0.0.0-20260411013819-759bbc3e3207.

**Is there a fix for CVE-2026-40890?** Yes. github.com/gomarkdown/markdown (Go): upgrade to 0.0.0-20260411013819-759bbc3e3207 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-40890?** Check whether you run github.com/gomarkdown/markdown (Go) or Gomarkdown Markdown at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/gomarkdown/markdown (Go): upgrade to 0.0.0-20260411013819-759bbc3e3207 or later

  ```sh
  go get github.com/gomarkdown/markdown@v0.0.0-20260411013819-759bbc3e3207
  ```


## Affected products

- github.com/gomarkdown/markdown (Go) < 0.0.0-20260411013819-759bbc3e3207, SEMVER:introduced=0,fixed=0.0.0-20260411013819-759bbc3e3207
- Gomarkdown Markdown

## Identifiers

- CVE-2026-40890
- GHSA-77fj-vx54-gvh7
- GO-2026-5208

## References

- [https://api.github.com/users/JulesDT](https://api.github.com/users/JulesDT)
- [https://github.com/JulesDT](https://github.com/JulesDT)
- [https://api.github.com/users/JulesDT/gists%7B/gist_id%7D](https://api.github.com/users/JulesDT/gists%7B/gist_id%7D)
- [https://api.github.com/users/JulesDT/repos](https://api.github.com/users/JulesDT/repos)
- [https://avatars.githubusercontent.com/u/14008484?v=4](https://avatars.githubusercontent.com/u/14008484?v=4)
- [https://api.github.com/users/JulesDT/events%7B/privacy%7D](https://api.github.com/users/JulesDT/events%7B/privacy%7D)

## Related threats

- [gomarkdown markdown IsSafeURL panic on short URLs](https://junglewise.ai/threats/cve-2026-102941-gomarkdown-markdown-issafeurl-panics-on-short-urls)
- [GO-2024-3205 - Infinite loop in github.com/gomarkdown/markdown](https://junglewise.ai/threats/cve-2024-44337-infinite-loop-in-github-com-gomarkdown-markdown)
- [GO-2023-2074 - Parser out-of-bounds read caused by a malformed markdown input in github.com/gomarkdown/markdown](https://junglewise.ai/threats/cve-2023-42821-markdown-vulnerable-to-out-of-bounds-read-while-parsing-citations)