Rust advisories / lz4_flex
Vulnerability HighRUSTSEC-2026-0041 · lz4_flex
RUSTSEC-2026-0041: Decompressing invalid data can leak information from uninitialized memory or reused output buffer
Short answerA security vulnerability in the lz4_flex crate: Decompressing invalid data can leak information from uninitialized memory or reused output buffer. GitHub rates it High. Fixed in 0.11.6, 0.12.1: update to a fixed version.
| Crate | lz4_flex |
|---|---|
| Type | Vulnerability (memory-exposure) |
| Affected versions | Before 0.11.6; from 0.12.0 before 0.12.1. |
| Fixed in | 0.11.6, 0.12.1 |
| Severity | High (GitHub rating) 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 |
| Published | 2026-03-17 |
| Last changed | 2026-03-17 |
| Also known as | CVE-2026-32829, GHSA-vvp9-7p8x-rfvv |
| Affected functions | lz4_flex::block::decompress, lz4_flex::block::decompress_into, lz4_flex::block::decompress_into_with_dict, lz4_flex::block::decompress_size_prepended, lz4_flex::block::decompress_size_prepended_with_dict, lz4_flex::block::decompress_with_dict |
What to do
- See which version you have:
cargo tree -i lz4_flex(it also shows which of your dependencies pulls it in). - Update within your version requirement:
cargo update -p lz4_flex. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for examplelz4_flex = "0.12.1") or update the dependency that pulls it in. - Check again with
cargo audit, or paste your Cargo.lock into our Cargo.toml checker.
Details from the advisory
Decompressing invalid LZ4 data with the block API can leak data from uninitialized memory, or leak content from previous decompression operations when reusing an output buffer.
The LZ4 block format defines a "match copy operation" which duplicates previously written data or data from a user-supplied dict. The position of that data is defined by an _offset_. lz4_flex did not properly validate _offset_ values, causing it to copy data from outside the initialized portion of the output buffer.
Two scenarios are affected:
- Decompressing with the
unsafeimplementation (safe-decodefeature flag disabled, which is the default): can leak content of uninitialized memory as part of the decompressed result. - Decompressing into a reused, user-supplied output buffer (also affects
safe-decode): can leak the previous contents of the output buffer as part of the decompressed result.
Only the block-based APIs are affected. All frame APIs are unaffected.
The flaw was corrected in versions 0.11.6 and 0.12.1 by properly validating offset values during decompression.
If upgrading is not possible, the issue can be mitigated by zeroing the output buffer before each call to the affected functions and enabling the safe-decode feature flag.
References
- Package: crates.io/crates/lz4_flex
- Advisory: rustsec.org/advisories/RUSTSEC-2026-0041.html
From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.
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