Use-after-free of a dictionary after a one-shot call on a context with an open stream

Overview

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.

Affected packages

• zstd-safe >= 3.0.1, < 8.2.0

Remediation

Upgrade to a patched release:

• zstd-safe 8.2.0