CVE-2026-49114

Summary

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.

Affected Software

Weaknesses

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

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: no
  • Technical Impact: partial

References

• https://github.com/onnx/onnx/security/advisories/GHSA-q56x-g2fj-4rj6
• https://raw.githubusercontent.com/cisagov/CSAF/develop/csaf_files/IT/white/2026/va-26-233-01.json
• https://www.cve.org/CVERecord?id=CVE-2026-49114

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