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10.0
CRITICAL CVSS 4.0
CVE-2026-15308
Incremental HTMLParser feed() allows CPU-exhaustion DoS via repeated unterminated markup declarations
Overview
Description

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

Details
INFO

Published Date :

July 9, 2026, 5:16 p.m.

Last Modified :

Aug. 11, 2026, 1:17 a.m.

Remotely Exploit :

Yes !

Source :

[email protected]
Impact
Affected Products

The following products are affected by CVE-2026-15308 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

ID Vendor Product Action
1 Python python
2 Python cpython
1 Python_software_foundation cpython
: Total Affected Vendor : 2 | Products : 3
Scoring
CVSS Scores
The Common Vulnerability Scoring System is a standardized framework for assessing the severity of vulnerabilities in software and systems. We collect and displays CVSS scores from various sources for each CVE.
Score Version Severity Vector Exploitability Score Impact Score Source
CVSS 134c704f-9b21-4f2e-91b3-4a467353bcc0
CVSS 3.1 HIGH [email protected]
CVSS 4.0 CRITICAL 28c92f92-d60d-412d-b760-e73465c3df22
CVSS 4.0 CRITICAL [email protected]
CVSS 4.0 HIGH [email protected]
Solution
Prevent DoS by sanitizing input or updating the parser.
  • Sanitize all HTML input data.
  • Update to a fixed version of the HTML parser.
Public PoC/Exploit Available at Github

CVE-2026-15308 has a 1 public PoC/Exploit available at Github. Go to the Public Exploits tab to see the list.

References
References to Advisories, Solutions, and Tools

Here, you will find a curated list of external links that provide in-depth information, practical solutions, and valuable tools related to CVE-2026-15308.

URL Resource
https://github.com/python/cpython/commit/07efb08123ba9367a7107325adb9d5626dca1ca9 Patch
https://github.com/python/cpython/commit/1e7956f1a722df9aabc509c30f8fbdc3a2b4fdc7
https://github.com/python/cpython/commit/785df8f743800661961528970f8598edcd291c14
https://github.com/python/cpython/commit/7933f4bf7131aa4140750f9404f5de0aa2969ced Patch
https://github.com/python/cpython/commit/bcf98ddbc40ec9b3ee87da0124a5660b19b7e606 Patch
https://github.com/python/cpython/commit/c2390b9376e35a701ed3acc597b8fc87546c9b00
https://github.com/python/cpython/commit/e9f92ac0b298292e7ff998e52cb8ccacfb27a0bd Patch
https://github.com/python/cpython/issues/153030 Patch
https://github.com/python/cpython/pull/153031 Issue Tracking Patch
https://mail.python.org/archives/list/[email protected]/thread/F6453LWKSHKCTWFLCOURWPLETNUIW2Z5/ Mailing List
http://www.openwall.com/lists/oss-security/2026/07/09/4 Third Party Advisory
CWE - Common Weakness Enumeration

While CVE identifies specific instances of vulnerabilities, CWE categorizes the common flaws or weaknesses that can lead to vulnerabilities. CVE-2026-15308 is associated with the following CWEs:

Common Attack Pattern Enumeration and Classification (CAPEC)

Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2026-15308 weaknesses.

We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).

Profile Photo
jaydarkseed757/rh-cve-pull

pull CVE to JSON from red hat.

Python

Updated: 3 weeks, 4 days ago
0 stars 0 fork 0 watcher
Born at : June 1, 2026, 12:54 p.m. This repo has been linked 3 different CVEs too.

Results are limited to the first 15 repositories due to potential performance issues.

The following list is the news that have been mention CVE-2026-15308 vulnerability anywhere in the article.

Results are limited to the first 20 news articles due to potential performance issues.

The following table lists the changes that have been made to the CVE-2026-15308 vulnerability over time.

Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.

  • CVE Modified by [email protected]

    Aug. 11, 2026

    Action Type Old Value New Value
    Added Reference https://github.com/python/cpython/commit/1e7956f1a722df9aabc509c30f8fbdc3a2b4fdc7
    Added Reference https://github.com/python/cpython/commit/c2390b9376e35a701ed3acc597b8fc87546c9b00
  • CVE Modified by [email protected]

    Aug. 06, 2026

    Action Type Old Value New Value
    Changed Affected [{'repo': 'https://github.com/python/cpython', 'vendor': 'Python Software Foundation', 'modules': ['html.parser', 'html'], 'product': 'CPython', 'versions': [{'status': 'affected', 'version': '0', 'lessThan': '3.14.7', 'versionType': 'python'}, {'status': 'affected', 'version': '3.15.0a1', 'lessThan': '3.15.0b4', 'versionType': 'python'}], 'defaultStatus': 'unaffected'}] [{'repo': 'https://github.com/python/cpython', 'vendor': 'Python Software Foundation', 'modules': ['html.parser', 'html'], 'product': 'CPython', 'versions': [{'status': 'affected', 'version': '0', 'lessThan': '3.13.15', 'versionType': 'python'}, {'status': 'affected', 'version': '3.14.0', 'lessThan': '3.14.7', 'versionType': 'python'}, {'status': 'affected', 'version': '3.15.0a1', 'lessThan': '3.15.0b4', 'versionType': 'python'}], 'defaultStatus': 'unaffected'}]
  • CVE Modified by [email protected]

    Aug. 05, 2026

    Action Type Old Value New Value
    Changed Affected [{'repo': 'https://github.com/python/cpython', 'vendor': 'Python Software Foundation', 'modules': ['html.parser', 'html'], 'product': 'CPython', 'versions': [{'status': 'affected', 'version': '0', 'lessThan': '3.15.0b4', 'versionType': 'python'}], 'defaultStatus': 'unaffected'}] [{'repo': 'https://github.com/python/cpython', 'vendor': 'Python Software Foundation', 'modules': ['html.parser', 'html'], 'product': 'CPython', 'versions': [{'status': 'affected', 'version': '0', 'lessThan': '3.14.7', 'versionType': 'python'}, {'status': 'affected', 'version': '3.15.0a1', 'lessThan': '3.15.0b4', 'versionType': 'python'}], 'defaultStatus': 'unaffected'}]
  • CVE Modified by [email protected]

    Aug. 05, 2026

    Action Type Old Value New Value
    Added Reference https://github.com/python/cpython/commit/785df8f743800661961528970f8598edcd291c14
  • CVE Modified by [email protected]

    Jul. 23, 2026

    Action Type Old Value New Value
    Changed Affected [{'repo': 'https://github.com/python/cpython', 'vendor': 'Python Software Foundation', 'modules': ['html.parser', 'html'], 'product': 'CPython', 'versions': [{'status': 'affected', 'version': '0', 'lessThan': '3.15.0', 'versionType': 'python'}], 'defaultStatus': 'unaffected'}] [{'repo': 'https://github.com/python/cpython', 'vendor': 'Python Software Foundation', 'modules': ['html.parser', 'html'], 'product': 'CPython', 'versions': [{'status': 'affected', 'version': '0', 'lessThan': '3.15.0b4', 'versionType': 'python'}], 'defaultStatus': 'unaffected'}]
  • Initial Analysis by [email protected]

    Jul. 10, 2026

    Action Type Old Value New Value
    Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
    Added CWE NVD-CWE-noinfo
    Added CPE Configuration OR *cpe:2.3:a:python:python:*:*:*:*:*:*:*:* versions up to (excluding) 3.15.0
    Added Reference Type Python Software Foundation: https://github.com/python/cpython/commit/07efb08123ba9367a7107325adb9d5626dca1ca9 Types: Patch
    Added Reference Type Python Software Foundation: https://github.com/python/cpython/commit/7933f4bf7131aa4140750f9404f5de0aa2969ced Types: Patch
    Added Reference Type Python Software Foundation: https://github.com/python/cpython/commit/bcf98ddbc40ec9b3ee87da0124a5660b19b7e606 Types: Patch
    Added Reference Type Python Software Foundation: https://github.com/python/cpython/commit/e9f92ac0b298292e7ff998e52cb8ccacfb27a0bd Types: Patch
    Added Reference Type Python Software Foundation: https://github.com/python/cpython/issues/153030 Types: Patch
    Added Reference Type Python Software Foundation: https://github.com/python/cpython/pull/153031 Types: Issue Tracking, Patch
    Added Reference Type Python Software Foundation: https://mail.python.org/archives/list/[email protected]/thread/F6453LWKSHKCTWFLCOURWPLETNUIW2Z5/ Types: Mailing List
    Added Reference Type CVE: http://www.openwall.com/lists/oss-security/2026/07/09/4 Types: Third Party Advisory
  • CVE Modified by af854a3a-2127-422b-91ae-364da2661108

    Jul. 09, 2026

    Action Type Old Value New Value
    Added Reference http://www.openwall.com/lists/oss-security/2026/07/09/4
  • CVE Modified by [email protected]

    Jul. 09, 2026

    Action Type Old Value New Value
    Added CVSS V4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/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
    Removed 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/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
  • CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Jul. 09, 2026

    Action Type Old Value New Value
    Added SSVC {'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'}
  • CVE Modified by [email protected]

    Jul. 09, 2026

    Action Type Old Value New Value
    Added Reference https://github.com/python/cpython/commit/07efb08123ba9367a7107325adb9d5626dca1ca9
    Added Reference https://github.com/python/cpython/commit/7933f4bf7131aa4140750f9404f5de0aa2969ced
    Added Reference https://github.com/python/cpython/commit/bcf98ddbc40ec9b3ee87da0124a5660b19b7e606
    Added Reference https://github.com/python/cpython/commit/e9f92ac0b298292e7ff998e52cb8ccacfb27a0bd
    Changed Affected [{'repo': 'https://github.com/python/cpython', 'vendor': 'Python Software Foundation', 'modules': ['html.parser', 'html'], 'product': 'CPython', 'versions': [{'status': 'affected', 'version': '0', 'lessThan': '3.16.0', 'versionType': 'python'}], 'defaultStatus': 'unaffected'}] [{'repo': 'https://github.com/python/cpython', 'vendor': 'Python Software Foundation', 'modules': ['html.parser', 'html'], 'product': 'CPython', 'versions': [{'status': 'affected', 'version': '0', 'lessThan': '3.15.0', 'versionType': 'python'}], 'defaultStatus': 'unaffected'}]
  • New CVE Received by [email protected]

    Jul. 09, 2026

    Action Type Old Value New Value
    Added Affected [{'repo': 'https://github.com/python/cpython', 'vendor': 'Python Software Foundation', 'modules': ['html.parser', 'html'], 'product': 'CPython', 'versions': [{'status': 'affected', 'version': '0', 'lessThan': '3.16.0', 'versionType': 'python'}], 'defaultStatus': 'unaffected'}]
    Added Description The incremental HTML parser (html.parser.HTMLParser) allows for CPU denial-of-service through repeated unterminated markup declarations when processing uncontrolled data.
    Added 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/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
    Added CWE CWE-400
    Added Reference https://github.com/python/cpython/issues/153030
    Added Reference https://github.com/python/cpython/pull/153031
    Added Reference https://mail.python.org/archives/list/[email protected]/thread/F6453LWKSHKCTWFLCOURWPLETNUIW2Z5/
EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days. Following chart shows the EPSS score history of the vulnerability.
CVSS
Vulnerability Scoring Details
Base CVSS Score: 10
Attack Vector
Attack Complexity
Attack Requirements
Privileges Required
User Interaction
VS Confidentiality
VS Integrity
VS Availability
SS Confidentiality
SS Integrity
SS Availability
Base CVSS Score: 7.5
Attack Vector
Attack Complexity
Privileges Required
User Interaction
Scope
Confidentiality Impact
Integrity Impact
Availability Impact