CVE-2026-4372: Arbitrary Remote Code Execution via `_attn_implementation_internal` Config Injection in huggingface/transformers

Vulnerability summary

CVE-2026-4372 is a high (CVSS 7.8) Missing Serialization Control Element vulnerability in huggingface huggingface/transformers. EPSS estimates a 0.70% chance of exploitation in the next 30 days, higher than 53% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 24-05-2026
   PublishedVulnerability first disclosed.
2. 26-05-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-1066Missing Serialization Control ElementThe product contains a serializable data element that does not have an associated serialization method.
• CWE-502Deserialization of Untrusted DataThe product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.