CVE-2025-6069: HTMLParser quadratic complexity when processing malformed inputs
CVE-2025-6069 is a vulnerability in HTMLParser quadratic complexity when processing malformed inputs, rated Moderate by Microsoft, with a CVSS 3.1 base score of 4.3 (Medium). An attacker can exploit it remotely over the network, with low privileges and without user interaction. Microsoft has not reported exploitation in the wild. The EPSS model estimates a 0.60% probability of exploitation activity in the next 30 days, higher than 49% of all scored vulnerabilities. Microsoft released the fix on 17 July 2025, outside Patch Tuesday. It affects 4 products in 2 product families (Mariner, Open Source Software).
Key facts
- CVE ID
- CVE-2025-6069
- Severity
- Medium CVSS 4.3
- Microsoft severity
- Moderate
- Exploited in the wild
- No
- Publicly disclosed
- No
- Weakness
- CWE-1333
- EPSS
- 0.60% (percentile 49%)
- CISA KEV
- Not listed
- Released
- Last updated
- Patch Tuesday
- June 2025 Patch Tuesday
- Product families
- Mariner, Open Source Software
CVSS score and vector
Microsoft scores CVE-2025-6069 at 4.3 (temporal 4.3) using CVSS 3.1. Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
| Metric | Value |
|---|---|
| Attack vector | Network |
| Attack complexity | Low |
| Privileges required | Low |
| User interaction | None |
| Scope | Unchanged |
| Confidentiality impact | None |
| Integrity impact | None |
| Availability impact | Low |
Frequently asked questions (Microsoft)
Is Azure Linux the only Microsoft product that includes this open-source library and is therefore potentially affected by this vulnerability?
One of the main benefits to our customers who choose to use the Azure Linux distro is the commitment to keep it up to date with the most recent and most secure versions of the open source libraries with which the distro is composed. Microsoft is committed to transparency in this work which is why we began publishing CSAF/VEX in October 2025. See this blog post for more information. If impact to additional products is identified, we will update the CVE to reflect this.
Affected products (4)
Mariner
| Product | Security update | Type | Fixed build | Restart |
|---|---|---|---|---|
| cbl2 python3 3.9.19-14 on CBL Mariner 2.0 | CBL-Mariner Releases | Security Update | 3.9.19-14 | No |
| azl3 python3 3.12.9-3 on Azure Linux 3.0 | CBL-Mariner Releases | Security Update | 3.12.9-3 | No |
Open Source Software
| Product | Security update | Type | Fixed build | Restart |
|---|---|---|---|---|
| cbl2 python3 3.9.19-13 on CBL Mariner 2.0 | CBL-Mariner Releases | Security Update | 3.9.19-14 | No |
| cbl2 python3 3.9.19-13 on CBL-Mariner 2.0 | CBL-Mariner Releases | Security Update | 3.9.19-14 | No |
NIST NVD data
- NVD status
- Deferred
- NVD CVSS
- 4.3 (MEDIUM)
- NVD weakness
- CWE-1333
- Published to NVD
- NVD last modified
References
- https://github.com/python/cpython/commit/4455cbabf991e202185a25a631af206f60bbc949
- https://github.com/python/cpython/commit/6eb6c5dbfb528bd07d77b60fd71fd05d81d45c41
- https://github.com/python/cpython/commit/8d1b3dfa09135affbbf27fb8babcf3c11415df49
- https://github.com/python/cpython/commit/ab0893fd5c579d9cea30841680e6d35fc478afb5
- https://github.com/python/cpython/commit/d851f8e258c7328814943e923a7df81bca15df4b
- https://github.com/python/cpython/commit/f3c6f882cddc8dc30320d2e73edf019e201394fc
- https://github.com/python/cpython/commit/fdc9d214c01cb4588f540cfa03726bbf2a33fc15
- https://github.com/python/cpython/issues/135462
- https://github.com/python/cpython/pull/135464
- https://mail.python.org/archives/list/security-announce@python.org/thread/K5PIYLR6EP3WR7ZOKKYQUWEDNQVUXOYM/
Revision history
| Version | Date | Description |
|---|---|---|
| 1.0 | Information published. | |
| 2.0 | Added python3 to Azure Linux 3.0 Added python3 to CBL-Mariner 2.0 | |
| 2.1 | Information published. | |
| 3.0 | Information published. |