CVE-2026-49114

ONNX symlink-following and path-traversal arbitrary file write

State: Published
Severity: 6.8 Medium
Published: Aug 21, 2026
Updated: Aug 21, 2026
Reserved: May 27, 2026

Description

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.

Scores

CVSS	Score	Vector	Source
4.0	6.8 Medium	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	cisa-cg
3.1	7.1 High	CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H	cisa-cg

Weaknesses

CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition
CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
CWE-59 Improper Link Resolution Before File Access ('Link Following')

Affected Products

Product	Versions
ONNXONNX	before 1.21.0Affected 1.21.0Not affected

References

urlvendor-advisoryexploit
urlthird-party-advisory
urlvdb-entry

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