CVE-2026-66038: ffmpeg Use of Uninitialized Resource
Vulnerability summary
CVE-2026-66038 is a high (CVSS 7.1) Use of Uninitialized Resource vulnerability in ffmpeg. EPSS estimates a 0.24% chance of exploitation in the next 30 days, higher than 14.3% of scored vulnerabilities.
Advisory lineage
Upstream 0 · Downstream 11 · Related 10Timeline
- 24-07-2026PublishedVulnerability first disclosed.
- 28-07-2026Last modifiedVulnerability information updated.
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.
CVSS metrics
9 scores · 6 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated7.1HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
- OSV · WolfiEcosystem advisory · calculated7.1HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
- OSV · ChainguardEcosystem advisory · calculated7.1HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
- NVDNIST7.1HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- OSV · UbuntuEcosystem advisory · calculated6.5MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
- OSV · DebianEcosystem advisory · calculated6.5MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
- NVDNIST6.5MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
EPSS trend
Probability
0.24%
Chance of exploitation in the next 30 days
Percentile
14%
Versus all other CVEs
30-day change
0.00 pp
From 0.24% on 18-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Chainguard18 products
- eco-python-ffmpeg-6-minimalAll versions (No fix recorded)
- eco-python-ffmpeg-6-minimal-devAll versions (No fix recorded)
- eco-python-ffmpeg-6-minimal-staticAll versions (No fix recorded)
- eco-python-ffmpeg-7-minimalAll versions (No fix recorded)
- eco-python-ffmpeg-7-minimal-devAll versions (No fix recorded)
Wolfi4 products
- ffmpeg-7All versions (No fix recorded)
- ffmpeg-7.1All versions (No fix recorded)
- ffmpeg-8.0All versions (No fix recorded)
- ffmpeg-8.1< 8.1.3-r0
Ubuntu2 products
- ffmpeg< 7:2.8.17-0ubuntu0.1+esm15 | < 7:3.4.11-0ubuntu0.1+esm13 | < 7:4.2.7-0ubuntu0.1+esm14 | < 7:4.4.2-0ubuntu0.22.04.1+esm13 | < 7:6.1.1-3ubuntu5+esm11 | All versions (No fix recorded) | < 7:8.0.1-3ubuntu2+esm3
- libavAll versions (No fix recorded)
Debian1 product
- ffmpegAll versions (No fix recorded) | < 7:9.0.2-1
Ffmpeg1 product
- ffmpeg≤ 8.1.2
5 vendors · 26 products
References
11 links- www.vulncheck.com/advisories/ffmpeg-lcl-zlib-video-decoder-information-disclosure-via-lcldec-cThird Party AdvisoryREPORTAdvisory
