# CVE-2026-41509: Integer underflow in crypto_sign_open() leads to buffer overflow

> An integer underflow in the CROSS signature library causes a buffer overflow, potentially allowing attackers to execute arbitrary code or crash the application.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 8 May 2026
- **Updated:** 8 May 2026
- **Also known as:** GHSA-w72c-hgx8-p7cv

## What is CVE-2026-41509?

CVE-2026-41509 is a medium-severity vulnerability in CROSS-signature CROSS-implementation, published on 8 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

CROSS implementation contains reference and optimized implementations of the CROSS post-quantum signature algorithm. Prior to commit fc6b7e7, there is a buffer overflow in crypto_sign_open() caused by an underflow of the integer mlen. This issue has been patched via commit fc6b7e7.

Weakness: CWE-122 (Heap-based Buffer Overflow), CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2026-41509?

It affects 1 product.


Products: Cross-Crypto Cross-Implementation.

## How do I fix CVE-2026-41509?

No fix has been published for CVE-2026-41509 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-41509 being exploited?

There is no known exploitation of CVE-2026-41509 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-41509 and fix it if it is affected.

What it is: CVE-2026-41509 is a medium-severity vulnerability in CROSS-signature CROSS-implementation, published on 8 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-41509 in the wild and no public exploit code.

Affected product: CROSS-signature CROSS-implementation. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-41509/ (Markdown: https://insights.sbomify.com/CVE-2026-41509/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-41509
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-41509
- OSV: https://osv.dev/vulnerability/CVE-2026-41509

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-41509/
Summaries are generated and may contain mistakes; the official description above is the record.