high CVSS 7.8 EPSS <0.1%

CVE-2026-4372·Python vulnerability

A critical remote code execution vulnerability exists in all versions of the HuggingFace transformers library prior to version 5.3.0. The vulnerability allows an attacker to craft a malicious `config.json` file containing the `_attn_implementation_internal` field set to an attacker-controlled HuggingFace Hub repository ID. When a victim loads this model using the standard `AutoModelForCausalLM.from_pretrained()` API, the library downloads and executes arbitrary Python code from the attacker's repository with the victim's full OS privileges. This issue arises due to unfiltered deserialization of configuration attributes, insufficient sanitization of internal fields, and unsandboxed execution of downloaded kernels. The vulnerability bypasses the `trust_remote_code` security mechanism, is invisible to the victim, and exploits the standard documented usage pattern, making it particularly severe. Users are advised to upgrade to version 5.3.0 or later to mitigate this issue.

Severity
high
Software
Python
Fixed in
5.3.0
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at <0.1% — higher than 9% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2026-4372 scores 7.8 on CVSS, so a successful attack would be serious — but at <0.1%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

Until: 5.3.0

Fixed in: 5.3.0

How to fix this CVE

Upgrade the HuggingFace transformers library to version 5.3.0 or later to patch a critical deserialization vulnerability that allows arbitrary code execution through malicious model configuration files. Update Python and all dependent packages immediately, then validate that no untrusted model configurations have been loaded in your environment. After patching, review any recently downloaded models from external sources for signs of compromise.

sudo dnf update python3-transformers || sudo pip3 install --upgrade transformers>=5.3.0

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed transformers version: python3 -c "import transformers; print(transformers.__version__)"
  2. Verify if transformers is installed via pip: pip3 show transformers | grep Version
  3. Audit model loading operations in application logs for calls to AutoModelForCausalLM.from_pretrained() with external model repositories
  4. Confirm the patch: python3 -c "import transformers; print('Patched' if transformers.__version__ >= '5.3.0' else 'Vulnerable')" && pip3 show transformers

FAQ

What is CVE-2026-4372?

CVE-2026-4372 is a critical code execution flaw in HuggingFace transformers library that allows attackers to embed malicious Python code in model configuration files. When victims load these models using standard APIs, the attacker's code executes with full OS privileges, bypassing security checks.

Is CVE-2026-4372 being actively exploited?

No, this vulnerability is not currently listed on CISA's Known Exploited Vulnerabilities (KEV) catalog, and no public exploits have been disclosed, though the attack vector is straightforward.

What versions of Python are affected by CVE-2026-4372?

All versions of the HuggingFace transformers library prior to version 5.3.0 are affected, regardless of the Python version, as the vulnerability exists in the library itself rather than Python core.

How do I check if my server is vulnerable to CVE-2026-4372?

Run: pip3 show transformers | grep Version. If the version is below 5.3.0, your environment is vulnerable. Also check: python3 -c "from transformers import __version__; print(__version__)" to confirm installed version.

Does Defensia detect CVE-2026-4372?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the transformers library is installed on a monitored server, CVE-2026-4372 will appear in your dashboard with remediation steps.

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References

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