CVE-2025-6921: transformers DoS — Exploit & Fix

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.

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CVSS v3.1 Score

7.5

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-400 Uncontrolled Resource Consumption

Affected Products

Vendor	Product	Versions
huggingface	transformers	< 4.53.0

References

Advisories & Patches

https://github.com/huggingface/transformers/commit/47c34fba5c303576560cb29767efb452ff12b8be

Exploits

https://huntr.com/bounties/287d15a7-6e7c-45d2-8c05-11e305776f1f

Frequently Asked Questions

What is CVE-2025-6921? +

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. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2025-6921? +

CVE-2025-6921 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2025-6921? +

CVE-2025-6921 affects products from huggingface, specifically: transformers. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-6921? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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