CVE-2026-49114 ONNX CVE debrief

Who should care

Organizations and developers using ONNX versions before 1.21.0 should prioritize upgrading to 1.21.0 or later to address the vulnerability. This is especially critical for those handling sensitive data or with strict file access controls, as the vulnerability could allow unauthorized data appends to sensitive files. IT teams, security professionals, and developers responsible for maintaining and securing software environments that utilize ONNX should be aware of this vulnerability and take appropriate action.

Technical 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. The vulnerability is addressed in version 1.21.0, which includes fixes to prevent such attacks by ensuring proper handling of file paths and permissions.

Defensive priority

Organizations using ONNX versions before 1.21.0 should prioritize upgrading to 1.21.0 or later to address the vulnerability.

Recommended defensive actions

• Upgrade ONNX to version 1.21.0 or later
• Review and update affected applications and configurations
• Monitor for suspicious activity related to ONNX external data serialization
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

The CVE-2026-49114 record indicates a vulnerability in ONNX before version 1.21.0, where the 'save_external_data' function could be exploited by a local attacker to append to arbitrary files. The issue was fixed in version 1.21.0. Evidence is based on NVD and CVE.org records. Further verification is recommended to assess affected deployments, review official advisories, and plan vendor-supported updates or mitigations.

Official resources