CVE-2025-6638VulnerabilityPublished 12 Sep 2025

CVE-2025-6638: huggingface/transformers · ReDoS

Affects huggingface/transformersSource CVE Database V5

Not known to be exploited · CVSS 5.3 Medium : upgrade to 4.53.0 when convenient.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 3.0 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.5% chance of exploitation in 30 days – higher than 46% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 4.53.0

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 12 Sep 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-26.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade huggingface/transformers to 4.53.0.

Affected software

Product	Affected	Fixed in
huggingface huggingface/transformers	Affected >=4.52.4 <4.53.0	Fixed in 4.53.0

AI-suggested

European organizations should upgrade the Hugging Face Transformers library to version 4.53.0 or later, where the vulnerability has been fixed. If immediate upgrading is not feasible, organizations should implement input validation and sanitization to detect and reject malformed or suspicious language code patterns before they reach the vulnerable tokenizer method. Rate limiting and anomaly detection on text input endpoints can help mitigate the risk of exploitation by limiting the volume of potentially malicious inputs. Additionally, monitoring CPU usage and application performance metrics can provide early warning signs of attempted ReDoS attacks. For critical systems, consider isolating NLP processing components behind dedicated services with resource constraints (e.g., CPU quotas, timeouts) to prevent cascading failures. Security teams should also review deployment architectures to ensure that untrusted user inputs are not directly processed by vulnerable components without proper filtering. Finally, maintain awareness of updates from Hugging Face and related security advisories to promptly apply patches.

Description

A Regular Expression Denial of Service (ReDoS) vulnerability was discovered in the Hugging Face Transformers library, specifically affecting the MarianTokenizer's `remove_language_code()` method. This vulnerability is present in version 4.52.4 and has been fixed in version 4.53.0. The issue arises from inefficient regex processing, which can be exploited by crafted input strings containing malformed language code patterns, leading to excessive CPU consumption and potential denial of service.

Impact

For European organizations, the impact primarily concerns availability disruptions in NLP-driven services or applications that integrate the Hugging Face Transformers library, particularly the MarianTokenizer component. Organizations leveraging these models for language translation, chatbots, content moderation, or other AI-driven text processing could experience service degradation or denial of service if exposed to crafted inputs exploiting this vulnerability. This could affect customer-facing applications, internal automation, or data processing pipelines, potentially leading to operational interruptions and reputational damage. Since the vulnerability does not affect confidentiality or integrity, data breaches or unauthorized data manipulation are not direct concerns. However, denial of service conditions could impact critical services, especially in sectors like finance, healthcare, or government where NLP tools are increasingly integrated. The medium severity rating suggests that while the risk is not critical, it should be addressed promptly to maintain service reliability and prevent potential exploitation in production environments.

CWE-1333Inefficient Regular Expression Complexity (opens in a new tab)
Base weaknessLikelihood of exploit: High
The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.
Architecture and Design
Use regular expressions that do not support backtracking, e.g. by removing nested quantifiers.
System Configuration
Set backtracking limits in the configuration of the regular expression implementation, such as PHP's pcre.backtrack_limit. Also consider limits on execution time for the process.
Implementation
Do not use regular expressions with untrusted input. If regular expressions must be used, avoid using backtracking in the expression.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
Attack patterns
Regular Expression Exponential Blowup (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 12 Sep 2025, 10:48 UTC

WeaknessesCWE-1333

Technical details

References

Community reviews

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