HTMLParser quadratic complexity when processing malformed inputs
Priority LOW 21CWE-1333Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · Low
- Fix status
- Partial Red Hat: 13 fixed, 6 without a fix
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat. Impact type from CWE-1333.
Summary
The html.parser.HTMLParser class had worse-case quadratic complexity when processing certain crafted malformed inputs potentially leading to amplified denial-of-service.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00603 49th percentileScored 2026-11-07
Fix Partial CPython (Python Software Foundation): 3.9.24, 3.10.19, 3.11.14 +3Red Hat: 8 advisoriesRed Hat: 13 fixed, 6 without a fix
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Python Software Foundation | CPython | before 3.9.24; 3.10.0 to before 3.10.19; 3.11.0 to before 3.11.14; 3.12.0 to before 3.12.12; 3.13.0 to before 3.13.6; 3.14.0a1 to before 3.14.0b3 | 3.9.24, 3.10.19, 3.11.14, 3.12.12, 3.13.6, 3.14.0b3 | Patch available | CNA |
- CPython VendorPython Software Foundation Affected before 3.9.24; 3.10.0 to before 3.10.19; 3.11.0 to before 3.11.14; 3.12.0 to before 3.12.12; 3.13.0 to before 3.13.6; 3.14.0a1 to before 3.14.0b3 Fixed in 3.9.24, 3.10.19, 3.11.14, 3.12.12, 3.13.6, 3.14.0b3 Patch available CNA
CPE names Threatist (inferred) · 1
Inferred from how NVD named this product before; not given by a source.
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:python:python:*:*:*:*:*:*:*:* | — | — | python-pillow |
- cpe:2.3:a:python:python:*:*:*:*:*:*:*:* Versions — — ·python-pillow
Remediation
- Fix · CNA CPython (Python Software Foundation) Fixed in 3.9.24, 3.10.19, 3.11.14, 3.12.12, 3.13.6, 3.14.0b3
Red Hat 8 advisories
- RHSA-2026:76945 Released 2026-10-06 · Red Hat rating Importantpython3.9 security update
- Red Hat Enterprise Linux AppStream E4S (v.9.2) python-unversioned-command-3.9.16-1.el9_2.15, python3-devel-3.9.16-1.el9_2.15, python3-tkinter-3.9.16-1.el9_2.15
- Red Hat Enterprise Linux BaseOS E4S (v.9.2) python3-3.9.16-1.el9_2.15, python3-libs-3.9.16-1.el9_2.15, python3.9-3.9.16-1.el9_2.15
- RHSA-2026:74087 Released 2026-09-30 · Red Hat rating Importantpython3.9 security update
- Red Hat Enterprise Linux AppStream E4S (v.9.4) python-unversioned-command-3.9.18-3.el9_4.14, python3-devel-3.9.18-3.el9_4.14, python3-tkinter-3.9.18-3.el9_4.14
- Red Hat Enterprise Linux BaseOS E4S (v.9.4) python3-3.9.18-3.el9_4.14, python3-libs-3.9.18-3.el9_4.14, python3.9-3.9.18-3.el9_4.14
- RHSA-2026:1858 Released 2026-02-03 · Red Hat rating ImportantRed Hat Ceph Storage
- Red Hat Ceph Storage 7 registry.redhat.io/rhceph/rhceph-7-rhel9
Show 5 more Red Hat advisories
- RHSA-2026:1652 Released 2026-02-02 · Red Hat rating ImportantRed Hat Ceph Storage
- Red Hat Ceph Storage 8 registry.redhat.io/rhceph/rhceph-8-rhel9
- RHSA-2026:0685 Released 2026-01-15 · Red Hat rating ModerateRed Hat Update Infrastructure 5 security update
- Red Hat Update Infrastructure 5 registry.redhat.io/rhui5/cds-rhel9, registry.redhat.io/rhui5/haproxy-rhel9, registry.redhat.io/rhui5/installer-rhel9 +1
- RHSA-2026:0414 Released 2026-01-08 · Red Hat rating ImportantA Subscription Management tool for finding and reporting Red Hat product usage
- Red Hat Discovery 2 registry.redhat.io/discovery/discovery-server-rhel9, registry.redhat.io/discovery/discovery-ui-rhel9
- RHSA-2025:23342 Released 2025-12-18 · Red Hat rating Moderatepython3.9 security update
- Red Hat Enterprise Linux AppStream (v. 9) python-unversioned-command-3.9.25-2.el9_7, python3-devel-3.9.25-2.el9_7, python3-tkinter-3.9.25-2.el9_7
- Red Hat Enterprise Linux BaseOS (v. 9) python3-3.9.25-2.el9_7, python3-libs-3.9.25-2.el9_7, python3.9-3.9.25-2.el9_7
- Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) python3-3.9.25-2.el9_7, python3-debug-3.9.25-2.el9_7, python3-idle-3.9.25-2.el9_7 +2
- RHSA-2025:23530 Released 2025-12-18 · Red Hat rating Importantpython39:3.9 security update
- Red Hat Enterprise Linux AppStream (v. 8) PyYAML-5.4.1-1.module+el8.9.0+19644+d68f775d.src::python39:3.9, mod_wsgi-4.7.1-7.module+el8.10.0+23075+0aa18782.1.src::python39:3.9, numpy-1.19.4-3.module+el8.9.0+19644+d68f775d.src::python39:3.9 +47
- Red Hat Enterprise Linux CRB (v. 8) Cython-0.29.21-5.module+el8.9.0+19644+d68f775d.src::python39-devel:3.9, pybind11-2.7.1-1.module+el8.9.0+19644+d68f775d.src::python39-devel:3.9, pytest-6.0.2-2.module+el8.9.0+19644+d68f775d.src::python39-devel:3.9 +33
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 10 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 6 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 7 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 8 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 9 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux AI (RHEL AI) | Affected | No fix yet: Fix deferred |
| Red Hat Ceph Storage 7 | Fixed | RHSA-2026:1858 |
| Red Hat Ceph Storage 8 | Fixed | RHSA-2026:1652 |
| Red Hat Discovery 2 | Fixed | RHSA-2026:0414 |
| Red Hat Enterprise Linux AppStream (v. 8) | Fixed | RHSA-2025:23530 |
| Red Hat Enterprise Linux AppStream (v. 9) | Fixed | RHSA-2025:23342 |
| Red Hat Enterprise Linux AppStream E4S (v.9.2) | Fixed | RHSA-2026:76945 |
| Red Hat Enterprise Linux AppStream E4S (v.9.4) | Fixed | RHSA-2026:74087 |
| Red Hat Enterprise Linux BaseOS (v. 9) | Fixed | RHSA-2025:23342 |
| Red Hat Enterprise Linux BaseOS E4S (v.9.2) | Fixed | RHSA-2026:76945 |
| Red Hat Enterprise Linux BaseOS E4S (v.9.4) | Fixed | RHSA-2026:74087 |
| Red Hat Enterprise Linux CRB (v. 8) | Fixed | RHSA-2025:23530 |
| Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) | Fixed | RHSA-2025:23342 |
| Red Hat Update Infrastructure 5 | Fixed | RHSA-2026:0685 |
Not affected: 2 products
- Red Hat Ceph Storage 7
- Red Hat Ceph Storage 8
Timeline
- 2026-10-02 Threatist record created from CVE-2025-6069
- 2026-10-03 Alias added: GHSA-j5cc-6rx8-ff96
- 2026-10-07 Fix available: RHSA-2026:76945 · Red Hat
- 2026-10-07 Fix available: Red Hat Enterprise Linux AppStream E4S (v.9.2), Red Hat Enterprise Linux BaseOS E4S (v.9.2) · Red Hat
References
Patch 8
- https://github.com/python/cpython/pull/135464
- https://github.com/python/cpython/commit/4455cbabf991e202185a25a631af206f60bbc949
- https://github.com/python/cpython/commit/6eb6c5dbfb528bd07d77b60fd71fd05d81d45c41
- https://github.com/python/cpython/commit/d851f8e258c7328814943e923a7df81bca15df4b
- https://github.com/python/cpython/commit/8d1b3dfa09135affbbf27fb8babcf3c11415df49
- https://github.com/python/cpython/commit/ab0893fd5c579d9cea30841680e6d35fc478afb5
- https://github.com/python/cpython/commit/f3c6f882cddc8dc30320d2e73edf019e201394fc
- https://github.com/python/cpython/commit/fdc9d214c01cb4588f540cfa03726bbf2a33fc15
Advisory 1
More Python Software Foundation vulnerabilities
- TI-2024-07037 Quadratic complexity parsing cookies with backslashes CVSS 3.1HIGH 7.5
- TI-2024-11791 Bypass extraction filter to modify file metadata outside extraction directory CVSS 3.1MEDIUM 5.3
- TI-2024-00411 Quoted zip-bomb protection for zipfile CVSS 3.1MEDIUM 6.2
- TI-2026-13296 `HTTPPasswordMgr` can send saved HTTPS credentials via HTTP because of incorrect scheme matching CVSS 4.0MEDIUM 6.0
- TI-2024-06422 Email header injection due to unquoted newlines CVSS 3.1MEDIUM 5.5
- TI-2026-04606 Possible to hijack modules in current working directory CVSS 4.0MEDIUM 5.6
Sources
- CVE-2025-6069 · CVE Program
- CVE-2025-6069 · NVD
- FIRST EPSS
- GHSA-j5cc-6rx8-ff96 · GitHub Advisory Database · CC BY 4.0
- CVE-2025-6069 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences