security research

zer0d4y5

Vulnerability research by Elias Hasas. Mostly parsers, decompressors, and the assumptions that survive a patch.

Writeups

Walkthrough GNU gzip method · fuzzing · PoC 2026-08-27

Checking gzip's .lzh patch

Working notes from going through CVE-2026-41992's fix commit: where the aliasing is written down, why AddressSanitizer reported nothing on a real out of bounds read, the structure-aware generator, and shrinking a candidate to eight bytes. With the commands.

→ 6 candidates in 226 execs, 41 bytes down to 8
CVE-2026-41992 GNU gzip CWE-126 · 6.9 Medium 2026-08-27

One array, two lives

The first fix cleared gzip's poisoned Huffman arrays in the branch that crashed, not in the function that reads them, leaving a tree walk eleven lines below it reading 32 KB past the allocation. Measured across three upstream revisions with a layout-independent oracle.

→ fix landed upstream in e7378c2d · credited in gzip THANKS and the CVE record