CPython: Uncontrolled Resource Consumption
CVE-2026-15308 is a high-severity uncontrolled resource consumption vulnerability in CPython from Python Software Foundation, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 3.10.21, 3.11.16, 3.12.14 as the first without the flaw, so updating CPython to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.64% chance of exploitation within 30 days, higher than 51% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update CPython to 3.10.21 or 3.11.16 or 3.12.14 or 3.13.15, whichever matches your release line, or a later version.
- Update Python to 3.10.21 or 3.11.16 or 3.12.14 or 3.13.15, whichever matches your release line, or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Python Software Foundation | CPython | before 3.10.21; 3.11.0 up to, but not including, 3.11.16; 3.12.0 up to, but not including, 3.12.14; 3.13.0 up to, but not including, 3.13.15; 3.14.0 up to, but not including, 3.14.7; 3.15.0a1 up to, but not including, 3.15.0b4 | 3.10.21, 3.11.16, 3.12.14, 3.13.15, 3.14.7, 3.15.0b4 |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) | V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) | V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) | V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) | V3.1.7 and later | Not stated |
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) | V3.1.7 and later | Not stated |
| Python | Python | before 3.10.21; 3.11.0 up to, but not including, 3.11.16; 3.12.0 up to, but not including, 3.12.14; 3.13.0 up to, but not including, 3.13.15; 3.14.0 up to, but not including, 3.14.7; 3.15.0 | 3.10.21, 3.11.16, 3.12.14, 3.13.15, 3.14.7 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 8.7 | High | CNA (python.org) |
| CVSS 3.1 | 7.5 | High | NVD |
Official description
The incremental HTML parser (html.parser.HTMLParser) allows for CPU denial-of-service through repeated unterminated markup declarations when processing uncontrolled data.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Uncontrolled Resource Consumption
The product does not properly control the allocation and maintenance of a limited resource.
How developers prevent this class of flaw
- Ensure that protocols have specific limits of scale placed on them.
- Ensure that all failures in resource allocation place the system into a safe posture.
More Uncontrolled Resource Consumption vulnerabilities (CWE-400)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- github.com/python/cpython/commit/07efb08123ba9367a7107325adb9d5626dca1ca9
- github.com/python/cpython/commit/1e7956f1a722df9aabc509c30f8fbdc3a2b4fdc7
- github.com/python/cpython/commit/785df8f743800661961528970f8598edcd291c14
- github.com/python/cpython/commit/7933f4bf7131aa4140750f9404f5de0aa2969ced
- github.com/python/cpython/commit/bcf98ddbc40ec9b3ee87da0124a5660b19b7e606
- github.com/python/cpython/commit/c2390b9376e35a701ed3acc597b8fc87546c9b00
- github.com/python/cpython/commit/e9f92ac0b298292e7ff998e52cb8ccacfb27a0bd
- github.com/python/cpython/issues/153030
- github.com/python/cpython/pull/153031Issue Tracking
Third-party and government advisories
- openwall.com/lists/oss-security/2026/07/09/4Third Party Advisory
Other references
Other vulnerabilities in CPython
- 8.2 High severity
- 9.4 Critical severity
- 7.6 High severity
- 9.2 Critical severity
- 8.4 High severity
- 8.2 High severity
Recent Uncontrolled Resource Consumption vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.7 High severity
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