# CVE-2026-27821: GPAC NHML Demuxer (dmx_nhml.c) Vulnerable to Stack Buffer Overflow

> A stack buffer overflow in GPAC's NHML demuxer allows attackers to execute arbitrary code or cause denial of service via crafted files.

- **Severity:** High 7.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 26 Feb 2026
- **Updated:** 26 Feb 2026
- **Also known as:** DEBIAN-CVE-2026-27821, GHSA-q7qh-8r2r-q559, UBUNTU-CVE-2026-27821

## What is CVE-2026-27821?

CVE-2026-27821 is a high-severity memory corruption vulnerability in Gpac Gpac, published on 26 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

GPAC is an open-source multimedia framework. In versions up to and including 26.02.0, a stack buffer overflow occurs during NHML file parsing in `src/filters/dmx_nhml.c`. The value of the xmlHeaderEnd XML attribute is copied from att->value into szXmlHeaderEnd[1000] using strcpy() without any length validation. If the input exceeds 1000 bytes, it overwrites beyond the stack buffer boundary. Commit 9bd7137fded2db40de61a2cf3045812c8741ec52 patches the issue.

Weakness: CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2026-27821?

It affects 1 product.


Products: Gpac Gpac.

## How do I fix CVE-2026-27821?

No fix has been published for CVE-2026-27821 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-27821 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27821 exists.

## Other vulnerabilities in Gpac Gpac

- [CVE-2023-46427](https://insights.sbomify.com/CVE-2023-46427/): Null dereference in n/a (critical 9.8)
- [CVE-2023-46932](https://insights.sbomify.com/CVE-2023-46932/): Memory corruption in n/a (critical 9.8)
- [CVE-2022-36190](https://insights.sbomify.com/CVE-2022-36190/): Use after free in n/a (critical 9.8)
- [CVE-2021-28300](https://insights.sbomify.com/CVE-2021-28300/): Null dereference in n/a (critical 9.8)
- [CVE-2020-11558](https://insights.sbomify.com/CVE-2020-11558/): Use after free in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-27821 and fix it if it is affected.

What it is: CVE-2026-27821 is a high-severity memory corruption vulnerability in Gpac Gpac, published on 26 Feb 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-2026-27821 exists.

Affected product: Gpac Gpac. 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-2026-27821/ (Markdown: https://insights.sbomify.com/CVE-2026-27821/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27821
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27821
- OSV: https://osv.dev/vulnerability/CVE-2026-27821

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27821/
Summaries are generated and may contain mistakes; the official description above is the record.