In ONNX before 1.21.0, the 'save_external_data' function builds the external-data file path from the model's external_data location field and opens it for writing without 'O_NOFOLLOW/O_EXCL', after a non-atomic 'os.path.isfile()' check. A local attacker with write access to the directory where a victim serializes external data can deterministically pre-plant a symlink that is being followed, causing the victim's write to append to any file the victim can write, e.g. ~/.ssh/authorized_keys, cron files, or application configs. Fixed in 1.21.0.
Published: 2026-08-21
Updated: 2026-09-16
Named Vulnerability: GHSA-q56x-g2fj-4rj6Named Vulnerability: GHSA-486p-g8x4-77mg
Base Score: 6.6
Vector: CVSS2#AV:L/AC:L/Au:N/C:N/I:C/A:C
Severity: Medium
Base Score: 7.1
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
Severity: High
Base Score: 6.8
Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N
Severity: Medium
EPSS: 0.00159