Reported

October 16, 2026

Issued

October 26, 2026

Package

zstd-safe (crates.io)

Type

INFO Unsound

Categories

• memory-exposure

Keywords

#use-after-free #dictionary

References

• https://github.com/gyscos/zstd-rs/commit/d34502a0ed07f80ab2aa4c65059578e0466f2467
• https://github.com/gyscos/zstd-rs/pull/384

Patched

• >=8.2.0

Unaffected

• <3.0.1

Affected Functions

Version

zstd_safe::DCtx::decompress

• >=3.0.1, <8.2.0

zstd_safe::DCtx::decompress_using_ddict

• >=3.0.1, <8.2.0

zstd_safe::DCtx::decompress_using_dict

• >=3.0.1, <8.2.0

Description

The one-shot DCtx and CCtx methods assumed the C library resets the context, but it leaves an open stream as it is. When a stream was left unfinished on a context, a one-shot call such as decompress_using_dict could leave the context pointing at the dictionary borrowed for that call, and the next streaming call resumed the stream against it after it was freed: decompressed output then contained freed heap memory. On the compression side, the stream resumed against the one-shot call's buffers.

This requires an application to use one context for both streaming and one-shot calls without a reset in between. The flaw was corrected by resetting the session after one-shot calls whenever a stream may be open.

Advisory available under CC0-1.0 license.