CVE-2026-66038 (CVSS 6.5)

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.

Is your site exposed to CVE-2026-66038?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

6.5

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

EPSS — Exploit Prediction

0.0026

Probability of exploitation

0.17%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-908 CWE-908

References

Other References

https://code.ffmpeg.org/FFmpeg/FFmpeg/commit/e7cbfd1c507b57a806a5825b87d609963e862c8c https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/23626 https://www.vulncheck.com/advisories/ffmpeg-lcl-zlib-video-decoder-information-disclosure-via-lcldec-c

Frequently Asked Questions

What is CVE-2026-66038? +

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. It has a CVSS v3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2026-66038? +

CVE-2026-66038 has a CVSS v3.1 score of 6.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0026, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-66038? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-54604

OpenSlide is a C library for reading whole slide image files. Prior to 4.0.1, a behavior change in libtiff 4.7.1 …

CVE-2025-2329

In high traffic environments, a Silicon Labs OpenThread RCP (see impacted versions) fails to clear the SPI transmit buffer and …

CVE-2025-48513

Use of uninitialized resource within the AMD Platform Management Framework (PMF) could allow an attacker to read a uninitialized kernel …

CVE-2026-49425

The compat32 kevent() handler translates a 64-bit kevent struct into a stack- declared 32-bit struct. It did not first zero …

CVE-2026-49424

The Linux waitid() implementation translates a FreeBSD siginfo_t struct into a stack-declared Linux siginfo_t. It did not first zero the …

CVE-2026-85483

Use of uninitialized resource, Return of wrong status code vulnerability in Apache Thrift c_glib bindings. This issue affects Apache Thrift: …

CVE-2026-66038