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.
Published: 2026-08-21
Score: 6.8 Medium
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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History

Fri, 21 Aug 2026 17:45:00 +0000

Type Values Removed Values Added
First Time appeared Onnx
Onnx onnx
Vendors & Products Onnx
Onnx onnx

Fri, 21 Aug 2026 17:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 21 Aug 2026 16:15:00 +0000

Type Values Removed Values Added
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.
Title ONNX symlink-following and path-traversal arbitrary file write
Weaknesses CWE-22
CWE-367
CWE-59
References
Metrics cvssV3_1

{'score': 7.1, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H'}

cvssV4_0

{'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'}


cve-icon MITRE

Status: PUBLISHED

Assigner: cisa-cg

Published:

Updated: 2026-08-21T16:43:10.933Z

Reserved: 2026-05-27T16:19:04.848Z

Link: CVE-2026-49114

cve-icon Vulnrichment

Updated: 2026-08-21T16:42:56.342Z

cve-icon NVD

Status : Received

Published: 2026-08-21T16:17:17.863

Modified: 2026-08-21T17:16:31.203

Link: CVE-2026-49114

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-21T17:30:03Z

Weaknesses