What’s Vulnerable › Vulnerabilities

CVE-2025-6921: Regular Expression Denial of Service (ReDoS) in huggingface/transformers

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2025-09-23 · updated 2026-10-11
• Weakness: CWE-400

Description

The huggingface/transformers library, versions prior to 4.53.0, is vulnerable to Regular Expression Denial of Service (ReDoS) in the AdamWeightDecay optimizer. The vulnerability arises from the _do_use_weight_decay method, which processes user-controlled regular expressions in the include_in_weight_decay and exclude_from_weight_decay lists. Malicious regular expressions can cause catastrophic backtracking during the re.search call, leading to 100% CPU utilization and a denial of service. This issue can be exploited by attackers who can control the patterns in these lists, potentially causing the machine learning task to hang and rendering services unresponsive.

Affected products

• huggingface/transformers: before 4.53.0 — fixed in 4.53.0

How to fix

Upgrade to a fixed version: huggingface/transformers 4.53.0. Check the vendor advisory for mitigations.

References

• https://github.com/huggingface/transformers/commit/47c34fba5c303576560cb29767efb452ff12b8be
• https://huntr.com/bounties/287d15a7-6e7c-45d2-8c05-11e305776f1f

Get alerted when CVE-2025-6921 or the next vulnerability affects your stack