# 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.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 21 Apr 2026
- **Updated:** 21 Apr 2026
- **Also known as:** CLEANSTART-2026-FB77791, CLEANSTART-2026-GL95997, DEBIAN-CVE-2026-40890, GHSA-77fj-vx54-gvh7, GO-2026-5208, MINI-6mmg-2qhp-9px8, MINI-83gq-c8gm-78mx, MINI-83qg-8rhq-fxqj, MINI-q92v-4qmm-mh44, MINI-rfhw-5qg9-25rp, MINI-v6jw-mj8m-3q9x, UBUNTU-CVE-2026-40890

## 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 (Out-of-bounds Read)

## 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 | Ecosystem | 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: Gomarkdown Markdown.

## How do I fix CVE-2026-40890?

Upgrade github.com/gomarkdown/markdown to 0.0.0-20260411013819-759bbc3e3207 or later.

## 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

- [CVE-2023-42821](https://insights.sbomify.com/CVE-2023-42821/): github.com/gomarkdown/markdown Out-of-bounds Read while parsing citations (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40890 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40890 exists.

Affected packages and fixed versions:
- github.com/gomarkdown/markdown (Go): affected all versions; fixed in 0.0.0-20260411013819-759bbc3e3207
- github.com/gomarkdown/markdown (Go): affected all versions; fixed in 0.0.0-20260411013819-759bbc3e3207
- github.com/gomarkdown/markdown (Go): affected all versions; fixed in 0.0.0-20260411013819-759bbc3e3207

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-40890/ (Markdown: https://insights.sbomify.com/CVE-2026-40890/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40890
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40890
- OSV: https://osv.dev/vulnerability/CVE-2026-40890

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40890/
Summaries are generated and may contain mistakes; the official description above is the record.