FreeBSD -- Use-after-free in multi-threaded xz decoder

Problem Description:

A worker thread could free its input buffer after decoding, while the main thread might still be writing to it. This leads to an use-after-free condition on heap memory.

Impact:

An attacker may use specifically crafted .xz file to cause multi-threaded xz decoder to crash, or potentially run arbitrary code under the credential the decoder was executed.