CVE-2025-6069VulnerabilityPublished 17 Jun 2025Updated 31 Jul 2026

CVE-2025-6069: Python Software Foundation CPython · ReDoS

Affects Python Software Foundation CPythonSource CVE Database V5

Not known to be exploited · CVSS 4.3 Medium.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

4.3Medium

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

EPSS: 0.6% chance of exploitation in 30 days – higher than 48% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
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: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
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 17 Jun 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 2026-10-25.

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

Affected software

Product	Affected	Fixed in
PyPIcpython`pkg:pypi/cpython`Other threats	Affected =3.10.0 =3.11.0 =3.12.0 =3.13.0 =3.14.0	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Until a patch is available, users should consider limiting exposure of services that parse untrusted HTML input or apply other application-level mitigations to reduce the risk of denial-of-service.

Description

CVE-2025-6069 is a medium severity vulnerability in the Python Software Foundation's CPython implementation. The html.parser.HTMLParser class exhibits worst-case quadratic time complexity when processing certain crafted malformed inputs, which can lead to an amplified denial-of-service condition. This issue affects specific CPython versions including 3.10.0 through 3.14.0a1. No official patch or fix information is currently available.

Impact

An attacker can exploit this vulnerability by supplying crafted malformed inputs to the html.parser.HTMLParser class, causing the parser to consume excessive CPU resources due to quadratic complexity in regular expression processing. This can lead to denial-of-service conditions by amplifying resource exhaustion. There is no impact on confidentiality or integrity.

Summary

The vulnerability identified as CVE-2025-6069 involves inefficient regular expression complexity in the html.parser.HTMLParser class of CPython. When processing certain malformed inputs, the parser's algorithm exhibits quadratic time complexity, potentially allowing an attacker to cause a denial-of-service by amplifying resource consumption. This flaw is categorized under CWE-1333 (Inefficient Regular Expression Complexity). The affected versions explicitly include CPython 3.10.0, 3.11.0, 3.12.0, 3.13.0, 3.14.0, and 3.14.0a1. The CVSS v3.1 base score is 4.3, indicating medium severity, with network attack vector, low attack complexity, requiring low privileges, no user interaction, and impact limited to availability.

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

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 7 Aug 2026, 15:00 UTC

WeaknessesCWE-1333

Technical details

References

Community reviews

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