XZ is a compressed file format that stores data in a structured layout, including Streams, Blocks, and an Index. That structure helps compression tools reconstruct files efficiently, but it also means decompression software must parse attacker-controlled metadata correctly.
In cyber security, XZ matters because archive handlers are code paths that process untrusted input. If a parser misreads sizes, offsets, or block boundaries, a crafted XZ file can trigger crashes, memory corruption, or sometimes code execution. Defenders treat XZ like any other risky file format: keep decompression libraries patched, validate embedded parsers in software that bundles them, and treat unexpected archives as untrusted until they are opened safely.