CVE-2026-15308: Incremental HTMLParser feed() allows CPU-exhaustion DoS via repeated unterminated markup declarations

High severity · published Jul 9, 2026

CVE-2026-15308

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

7.5

CVSS

0.6%

EPSS

On KEV

Description

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

CVSS vector

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

Attack vector

Network

Complexity

Low

Privileges

None

User interaction

None

Confidentiality

None

Integrity

None

Availability

High

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)0.6% · higher than 50% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

CPython · Python Software Foundation

before 3.10.21; 3.11.0 before 3.11.16; 3.12.0 before 3.12.14; 3.13.0 before 3.13.15; 3.14.0 before 3.14.7; 3.15.0a1 before 3.15.0b4 · source: vendor

Python · Python

before 3.10.21; 3.11.0 before 3.11.16; 3.12.0 before 3.12.14; 3.13.0 before 3.13.15; 3.14.0 before 3.14.7; 3.15.0; +10 more · source: NVD

Affected product

CPython

Python Software Foundation

All CPython CVEs

References

NVD

https://nvd.nist.gov/vuln/detail/CVE-2026-15308

CVE.org

https://www.cve.org/CVERecord?id=CVE-2026-15308

Patch

https://github.com/python/cpython/commit/07efb08123ba9367a7107325adb9d5626dca1ca9

Patch

https://github.com/python/cpython/commit/1e7956f1a722df9aabc509c30f8fbdc3a2b4fdc7

Patch

https://github.com/python/cpython/commit/785df8f743800661961528970f8598edcd291c14

Patch

https://github.com/python/cpython/commit/7933f4bf7131aa4140750f9404f5de0aa2969ced

Patch

https://github.com/python/cpython/commit/bcf98ddbc40ec9b3ee87da0124a5660b19b7e606

Patch

https://github.com/python/cpython/commit/c2390b9376e35a701ed3acc597b8fc87546c9b00