CVE-2025-2099Public exploitNetwork attack vector

Service interruption via nested-quantifier regex backtracking

Published May 19, 2025 · Updated May 19, 2025

Regular expression denial of service in Hugging Face Transformers before 4.50.0 allows attackers to interrupt service through CPU exhaustion. The preprocess_string() function in transformers.testing_utils applies a nested-quantifier regex to docstring code blocks, causing exponential backtracking on inputs containing many newline characters. Reachability requires attacker-controlled text to reach preprocess_string() or a caller; CPU exhaustion can interrupt the hosting application.

CVSS severity7.5
High
EPSS probability0.58%
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 4.50.0 allows attackers to interrupt service through CPU exhaustion. The preprocess_string() function in transformers.testing_utils applies a nested-quantifier regex to docstring code blocks, causing exponential backtracking on inputs containing many newline characters. Reachability requires attacker-controlled text to reach preprocess_string() or a caller; CPU exhaustion can interrupt the hosting application.

The record

CVE
CVE-2025-2099
Published
May 19, 2025
Updated
May 19, 2025
Vendor
Hugging Face
Product
Hugging Face Transformers
Classifications
CWE-1333, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 19, 2025CVE publishedPublication date reported by the CVE source.
  2. May 19, 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 <4.50.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Hugging Face · Hugging Face Transformersversion=unspecified <4.50.0

Published CVSS scores

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

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 exploitPublished

Weakness, pattern, technique

CWE-1333Inefficient Regular Expression Complexity
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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