# CVE-2026-66038: FFmpeg LCL/ZLIB Video Decoder Information Disclosure via lcldec.c

> Attackers can expose uninitialized heap memory via crafted video streams, potentially leaking sensitive data and defeating ASLR in media processing services.

- **Severity:** High 7.1 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 24 Jul 2026
- **Updated:** 28 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-66038, ECHO-9db0-dfd3-a7bb, GHSA-8mx4-8xfc-qr43, JLSEC-2026-1184, MINI-xp5m-j82j-47c8, UBUNTU-CVE-2026-66038

## What is CVE-2026-66038?

CVE-2026-66038 is a high-severity vulnerability in Ffmpeg Ffmpeg, published on 24 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

FFmpeg through 8.1.2, fixed in commit 8670835, contains an information disclosure vulnerability in the LCL/ZLIB video decoder that allows attackers to expose uninitialized heap memory by supplying a valid zlib stream that inflates to fewer bytes than the expected frame size. The zlib_decomp() function in lcldec.c treats short decompression as non-fatal and continues to the RGB24 conversion path, which copies a full frame's worth of rows from the allocation buffer using original frame dimensions, causing uninitialized heap contents including pointer-derived allocator bytes to be copied into the attacker-observable AVFrame output and potentially defeating ASLR in long-lived media processing services.

Weakness: CWE-908 (Use of Uninitialized Resource)

## Which versions are affected by CVE-2026-66038?

It affects 1 product.


Products: Ffmpeg Ffmpeg.

## How do I fix CVE-2026-66038?

Apply the vendor's patch.

## Is CVE-2026-66038 being exploited?

There is no known exploitation of CVE-2026-66038 in the wild and no public exploit code.

## Other vulnerabilities in Ffmpeg Ffmpeg

- [CVE-2013-0864](https://insights.sbomify.com/CVE-2013-0864/): Memory corruption in n/a (critical 10.0)
- [CVE-2013-0872](https://insights.sbomify.com/CVE-2013-0872/): Memory corruption in n/a (critical 10.0)
- [CVE-2013-0873](https://insights.sbomify.com/CVE-2013-0873/): Memory corruption in n/a (critical 10.0)
- [CVE-2013-4265](https://insights.sbomify.com/CVE-2013-4265/): Null dereference in n/a (critical 10.0)
- [CVE-2011-3937](https://insights.sbomify.com/CVE-2011-3937/): Memory corruption in n/a (critical 10.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-66038 and fix it if it is affected.

What it is: CVE-2026-66038 is a high-severity vulnerability in Ffmpeg Ffmpeg, published on 24 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-66038 in the wild and no public exploit code.

Affected product: Ffmpeg Ffmpeg. 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-2026-66038/ (Markdown: https://insights.sbomify.com/CVE-2026-66038/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-66038
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-66038
- OSV: https://osv.dev/vulnerability/CVE-2026-66038

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-66038/
Summaries are generated and may contain mistakes; the official description above is the record.