published July 27, 2026
Relative Path Traversal vulnerability in Erlang OTP (stdlib zip module) allows writing files outside the intended extraction directory via a crafted zip archive.
zip:unzip/1,2 and zip:extract/1,2 validate entry paths using zip:check_dir_level/2, which tracks directory depth as a running integer counter: .. decrements it, normal path components increment it. The caller rejects only paths where the final counter value is less than zero. A path such as ../x/y causes the counter to go negative mid-traversal then recover to zero, passing validation while resolving to a location outside the extraction directory when joined with the current working directory via add_cwd.
This vulnerability is associated with program file lib/stdlib/src/zip.erl.
This issue affects OTP from OTP 27.1 before OTP 27.3.4.15, OTP 28.5.0.4, and OTP 29.0.4, corresponding to stdlib from 6.1 before 6.2.2.4, 7.3.0.1, and 8.0.3.