lz4_flex's decompression can leak information from uninitialized memory or reused output buffer

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.2 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-32829: 0.62% estimated exploitation activity in the next 30 days; percentile 49.72 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Decompressing invalid LZ4 data can leak data from uninitialized memory, or can leak content from previous decompression operations when reusing an output buffer. Details The LZ4 block format defines a "match copy operation" which duplicates previously written data or data from the user-supplied dict. The position of that data is defined by an offset. The data is copied within the output buffer from the offset to the current output position. However, lz4flex did not properly detect invalid and out-of-bounds offset values properly, causing it to copy uninitialized data from the output buffer. Only the block based API functions are affected: lz4flex::block::{decompressinto, decompressintowithdict} When safe-decode is disabled additionally these functions are affected lz4flex::block::{decompress, decompresswithdict, decompresssizeprepended, decompresssizeprependedwithdict} All frame APIs are not affected. There are two affected use cases: - decompressing LZ4 data with the unsafe…

Published by the source

16 Mar 2026, 20:48 UTC

Last modified by the source

20 Mar 2026, 21:18 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-vvp9-7p8x-rfvv

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# Patch Next advisory brief: CVE-2026-32829

Advisory: lz4_flex's decompression can leak information from uninitialized memory or reused output buffer
IDs: CVE-2026-32829, GHSA-vvp9-7p8x-rfvv
Record: https://patchnext.com/advisories/cve-2026-32829 (revision 1, source checked 26 Oct 2026, 15:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: lz4_flex 0.12.1, 0.11.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io lz4_flex: affected < 0.11.6; >= 0.12.0, < 0.12.1; fixed in 0.12.1, 0.11.6

## Suggested inspection (read-only)
- crates.io lz4_flex: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on lz4_flex.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-vvp9-7p8x-rfvv (GitHub-reviewed advisory GHSA-vvp9-7p8x-rfvv lists affected ranges: crates.io lz4_flex >=0 =0.12.0 <0.12.1)

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