CVE-2026-34445

The ExternalDataInfo class in ONNX was using Python’s setattr() function to load metadata (like file paths or data lengths) directly from an ONNX model file. The problem? It didn’t check if the "keys" in the file were valid. Because it blindly trusted the file, an attacker could craft a malicious model that overwrites internal object properties.

Why its Dangerous

Instant Crash DoS: An attacker can set the length property to a massive number like 9 petabytes. When the system tries to load the model, it attempts to allocate all that RAM at once, causing the server to crash or freeze Out of Memory.

Access Bypass: By setting a negative offset -1, an attacker can trick the system into reading parts of a file it wasn't supposed to touch.

Object Corruption: Attackers can even inject "dunder" attributes like class to change the object's type entirely, which could lead to more complex exploits.

Fixed: https://github.com/onnx/onnx/pull/7751 object state corruption and DoS via ExternalDataInfo attribute injection

The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.

CVE-2026-34445 has a CVSS score of 8.6 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.21.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-34445? CVE-2026-34445 is a high-severity improper input validation vulnerability in onnx (pip), affecting versions <= 1.20.1. It is fixed in 1.21.0. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
2. How severe is CVE-2026-34445? CVE-2026-34445 has a CVSS score of 8.6 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of onnx are affected by CVE-2026-34445? onnx (pip) versions <= 1.20.1 is affected.
4. Is there a fix for CVE-2026-34445? Yes. CVE-2026-34445 is fixed in 1.21.0. Upgrade to this version or later.
5. Is CVE-2026-34445 exploitable, and should I be worried? Whether CVE-2026-34445 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-34445 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-34445? Upgrade onnx to 1.21.0 or later.

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