CVE-2026-34743: XZ Utils: Buffer overflow in lzma_index_append()

XZ Utils provide a general-purpose data-compression library plus command-line tools. Prior to version 5.8.3, if lzmaindexdecoder() was used to decode an Index that contained no Records, the resulting lzmaindex was left in a state where where a subsequent lzmaindexappend() would allocate too little memory, and a buffer overflow would occur. This issue has been patched in version 5.8.3.

— MITRE

XZ Utils: Buffer overflow in lzmaindexappend()

— Microsoft