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CVE-2026-15308

Incremental HTMLParser feed() allows CPU-exhaustion DoS via repeated unterminated markup declarations

HIGH
7.5
CVSS Score
Published: July 9, 2026 at 05:10 PM UTC
Updated: October 25, 2026 at 05:10 PM UTC
1 product affected across 1 vendorPython

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Severity
HIGH7.5
Exploit prediction
EPSS 0.6%
SSVC
No known exploit

Description

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

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Python· Python
95%
v < 3.10.213.11.0 ≤ v < 3.11.163.12.0 ≤ v < 3.12.143.13.0 ≤ v < 3.13.153.14.0 ≤ v < 3.14.73.11.03.12.03.13.03.14.03.15.03.15.0 alpha13.15.0 alpha23.15.0 alpha33.15.0 alpha43.15.0 alpha53.15.0 alpha63.15.0 alpha73.15.0 alpha83.15.0 beta13.15.0 beta23.15.0 beta33.15.0a1
Affected range stops below 3.10.21, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.11.16, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.12.14, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.13.15, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.14.7, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.15.0b4, so it looks safe — our inference, not a vendor statement

References (11)

Issue TrackingPatch
Source: [email protected]
https://github.com/python/cpython/issues/153030
PatchIssue Tracking
Source: [email protected]
https://github.com/python/cpython/pull/153031
Vendor AdvisoryMailing List
Source: [email protected]
https://mail.python.org/archives/list/[email protected]/thread/F6453LWKSHKCTWFLCOURWPLETNUIW2Z5/
Patch
Source: cverecord
https://github.com/python/cpython/commit/07efb08123ba9367a7107325adb9d5626dca1ca9
Patch
Source: cverecord
https://github.com/python/cpython/commit/7933f4bf7131aa4140750f9404f5de0aa2969ced
Patch
Source: cverecord
https://github.com/python/cpython/commit/bcf98ddbc40ec9b3ee87da0124a5660b19b7e606
Patch
Source: cverecord
https://github.com/python/cpython/commit/e9f92ac0b298292e7ff998e52cb8ccacfb27a0bd
Third Party Advisory
Source: af854a3a-2127-422b-91ae-364da2661108
http://www.openwall.com/lists/oss-security/2026/07/09/4

SSVC — Action Prioritization

SSVCNo known exploitAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

7.5HIGH[email protected]
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Vector?

Quick Info

StatusANALYZED
CWE
CWE-400NVD-CWE-noinfo

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