CVE-2025-6921Network attack vector

Training-task hang via unbounded regex backtracking

Published Sep 23, 2025 · Updated Sep 23, 2025

Regular expression denial of service in Hugging Face Transformers before 4.53.0 allows attackers to hang training tasks via crafted patterns. AdamWeightDecay._do_use_weight_decay passes entries from its include and exclude lists directly to re.search, permitting catastrophic backtracking against parameter names. Reachability requires control of those optimizer pattern lists; exploitation saturates a processor and stalls the affected task without a reported data impact.

CVSS severity7.5
High
EPSS probability0.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Regular expression denial of service in Hugging Face Transformers before 4.53.0 allows attackers to hang training tasks via crafted patterns. AdamWeightDecay._do_use_weight_decay passes entries from its include and exclude lists directly to re.search, permitting catastrophic backtracking against parameter names. Reachability requires control of those optimizer pattern lists; exploitation saturates a processor and stalls the affected task without a reported data impact.

The record

CVE
CVE-2025-6921
Published
Sep 23, 2025
Updated
Sep 23, 2025
Vendor
Hugging Face
Product
Hugging Face Transformers
Classifications
CWE-400, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 23, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 23, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <4.53.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Hugging Face · Hugging Face Transformersversion=unspecified <4.53.0

Published CVSS scores

5.3huntr.devCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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