HighCVE-2026-15308

Python Software Foundation CPython: Uncontrolled Resource Consumption (CVE-2026-15308)

Published 09.07.2026Last modified 25.10.2026Sources: BSI, Red Hat, SUSE, CVE.org, Msrc Update Guide, OSV, Debian LTS, Ubuntu

What is affected, what to do

The incremental HTML parser (html.parser.HTMLParser) allows for CPU denial-of-service through repeated unterminated markup declarations when processing uncontrolled data.

Update Python Software Foundation CPython to version 3.10.21, Python Software Foundation CPython to version 3.11.16, Python Software Foundation CPython to version 3.12.14.

Affected: Python Software Foundation CPython lt *..3.10.21
Python Software Foundation CPython lt 3.11.0..3.11.16
Python Software Foundation CPython lt 3.12.0..3.12.14
Python Software Foundation CPython lt 3.13.0..3.13.15
Python Software Foundation CPython lt 3.14.0..3.14.7
Python Software Foundation CPython lt 3.15.0a1..3.15.0b4
Fixed in: Python Software Foundation CPython 3.10.21
Python Software Foundation CPython 3.11.16
Python Software Foundation CPython 3.12.14
Python Software Foundation CPython 3.13.15
Python Software Foundation CPython 3.14.7
Python Software Foundation CPython 3.15.0b4

Not sure whether and how you are affected? Ask a question about this vulnerability

Metrics

8.7

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: NVD, CVSS v4

7.5

CVSS v3

Severity High on the scale from 0 to 10.

Source: BSI, Red Hat, SUSE, CVE.org, Msrc Update Guide, OSV, Debian LTS, Ubuntu

0.6 %

EPSS score

Low — model estimates < 1% exploitation likelihood.

Source: FIRST EPSS, percentile 50.3

Show all metrics

Severity: High
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 84.24 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: no public PoC known
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 8.7 Methodology
CVSS v3 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 7.5
CVSS v4 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 8.7
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 0.6 %; Low — model estimates < 1% exploitation likelihood.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 50.3; High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: —
Published: 09.07.2026
CWE CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect. Read in glossary: CWE-400

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

The incremental HTML parser (html.parser.HTMLParser) allows for CPU denial-of-service through repeated unterminated markup declarations when processing uncontrolled data.

Source: BSI WID Portal, BSI CSAF, redhat_csaf, suse_csaf, NVD (NIST), Microsoft Security Update Guide, OSV (Open Source Vulnerabilities), cvelistv5, Debian LTS Advisories, Ubuntu Security Notices

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
Python Software Foundation	CPython	`3.12.0 – < 3.12.14` `3.11.0 – < 3.11.16` `3.13.0 – < 3.13.15` `< 3.10.21` `3.15.0a1 – < 3.15.0b4` `3.14.0 – < 3.14.7`	`3.12.14` `3.11.16` `3.13.15` `3.10.21` `3.15.0b4` `3.14.7`
python	python	`< 3.10.21` `3.11.0 – < 3.11.16` `3.15.0` `3.14.0 – < 3.14.7` `3.13.0 – < 3.13.15` `3.12.0 – < 3.12.14`	`3.10.21` `3.11.16` — `3.14.7` `3.13.15` `3.12.14`
IBM	App Connect Enterprise CD	`< 13.4.0`	`13.4.0`
IBM	App Connect Enterprise LTS	`< 13.4.0` `< 12.0.26`	`13.4.0` `12.0.26`
IBM	QRadar SIEM	`<7.5.0 UP15 IF06`	—
Open Source	Python CPython	`≤ 3.15.0`	—

Vendors and products

Affected operating systems

Affected operating systems

Linux	ubuntu	python2.7	`bionic`
Linux	ubuntu	python2.7	`focal`
Linux	ubuntu	python2.7	`jammy`
Linux	ubuntu	python2.7	`trusty`
Linux	ubuntu	python2.7	`xenial`
Linux	ubuntu	python3.10	`jammy`
Linux	debian	python3.11	`bookworm`
Linux	ubuntu	python3.11	`jammy`
Linux	ubuntu	python3.12	`noble`
Linux	ubuntu	python3.14	`resolute`
Linux	ubuntu	python3.4	`trusty`
Linux	ubuntu	python3.5	`trusty`
Linux	ubuntu	python3.5	`xenial`
Linux	ubuntu	python3.6	`bionic`
Linux	ubuntu	python3.7	`bionic`
Linux	ubuntu	python3.8	`bionic`
Linux	ubuntu	python3.8	`focal`
Linux	ubuntu	python3.9	`focal`

Weakness classes (CWE)

CWE-400Uncontrolled Resource Consumption
Class
The product does not properly control the allocation and maintenance of a limited resource.
Entry at MITRE CWE-400

References & sources

mail.python.orgarchives/list/security-announce@python.org/thread/F6453LWKSHKCT…advisory, Vendor advisory, Mailing list
github.compython/cpython/pull/153031web, Patch, Issue tracking, Patch
github.compython/cpython/issues/153030report, Issue tracking, Patch
github.compython/cpython/commit/07efb08123ba9367a7107325adb9d5626dca1ca9fix, Patch, Patch
github.compython/cpython/commit/7933f4bf7131aa4140750f9404f5de0aa2969cedfix, Patch, Patch
github.compython/cpython/commit/bcf98ddbc40ec9b3ee87da0124a5660b19b7e606fix, Patch, Patch
github.compython/cpython/commit/e9f92ac0b298292e7ff998e52cb8ccacfb27a0bdfix, Patch, Patch
github.compython/cpython/commit/785df8f743800661961528970f8598edcd291c14Patch, Patch
openwall.comlists/oss-security/2026/07/09/4Third-party advisory
github.compython/cpython/commit/1e7956f1a722df9aabc509c30f8fbdc3a2b4fdc7fix, Patch, Patch
github.compython/cpython/commit/c2390b9376e35a701ed3acc597b8fc87546c9b00fix, Patch, Patch
NVD (NIST)vuln/detail/CVE-2026-15308web

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

11.08.2026Record modifiedpython.org

New references:

Show 2 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://github.com/python/cpython/commit/1e7956f1a722df9aabc509c30f8fbdc3a2b4fdc7
Reference	added	—	https://github.com/python/cpython/commit/c2390b9376e35a701ed3acc597b8fc87546c9b00

Source identifier: cna@python.org

05.08.2026Record modifiedpython.org
1 individual change: Affected versions (publisher)
Show the original change
Individual changes of this event as published by NVD
Type Action Before After
Affected versions (publisher) changed
CPython
CPython
Source identifier: cna@python.org
23.07.2026Record modifiedpython.org
1 individual change: Affected versions (publisher)
Show the original change
Individual changes of this event as published by NVD
Type Action Before After
Affected versions (publisher) changed
CPython
CPython
Source identifier: cna@python.org

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	changed	CPython	CPython

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	changed	CPython	CPython

09.07.2026Record modifiedpython.org

New references:

Show 5 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://github.com/python/cpython/commit/07efb08123ba9367a7107325adb9d5626dca1ca9
Reference	added	—	https://github.com/python/cpython/commit/7933f4bf7131aa4140750f9404f5de0aa2969ced
Reference	added	—	https://github.com/python/cpython/commit/bcf98ddbc40ec9b3ee87da0124a5660b19b7e606
Reference	added	—	https://github.com/python/cpython/commit/e9f92ac0b298292e7ff998e52cb8ccacfb27a0bd
Affected versions (publisher)	changed	CPython	CPython

Source identifier: cna@python.org

09.07.2026Record modifiedCISA ADP

CISA assessment (SSVC): exploitation: none known, automatable: yes

Show the original change

Individual changes of this event as published by NVD
Type	Action	Before	After
SSVC assessment	added	—	{"id":"CVE-2026-15308","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-07-09T17:31:19.781935Z"}

Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

Show one older change

09.07.2026Receivedpython.org

CVSS V4.0: AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

Weakness type: CWE-400

Description added or changed

New references:

Show 7 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	CPython
Description	added	—	The incremental HTML parser (html.parser.HTMLParser) allows for CPU denial-of-service through repeated unterminated markup declarations when processing uncontrolled data.
CVSS	added	—	AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Weakness type (CWE)	added	—	CWE-400
Reference	added	—	https://github.com/python/cpython/issues/153030
Reference	added	—	https://github.com/python/cpython/pull/153031
Reference	added	—	https://mail.python.org/archives/list/security-announce@python.org/thread/F6453LWKSHKCTWFLCOURWPLETNUIW2Z5/

Source identifier: cna@python.org

One NVD translation into another language is hidden.

Linked advisories

@RISK®: The Consensus Security Vulnerability Alert: Vol. 26, Num. 27SANS @RISK16.07.2026

Embed badge

Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.

<a href="https://intel.neosec.eu/en/cve/CVE-2026-15308"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-15308.svg?lang=en" alt="CVE-2026-15308 – NEOSEC Intel" height="20"></a>