CPython: Improper Check for Certificate Revocation
CVE-2026-115557 is a critical-severity improper check for certificate revocation vulnerability in CPython from Python Software Foundation, with a CVSS 4.0 base score of 9.4 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. The record lists versions 3.11.18, 3.12.16, 3.13.18 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 0.53% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update CPython to 3.11.18 or 3.12.16 or 3.13.18 or 3.14.10, 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.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Python Software Foundation | CPython | before 3.11.18; 3.12.0 up to, but not including, 3.12.16; 3.13.0 up to, but not including, 3.13.18; 3.14.0 up to, but not including, 3.14.10; 3.15.0 up to, but not including, 3.15.2; 3.16.0a1 up to, but not including, 3.16.0 | 3.11.18, 3.12.16, 3.13.18, 3.14.10, 3.15.2, 3.16.0 |
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.
- Attack requirements
- NoneThe attack does not depend on a particular deployment or configuration.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- PassiveA user only needs to do something routine, such as viewing a page.
- Confidentiality (vulnerable system)
- HighSerious loss of confidentiality on the vulnerable system.
- Integrity (vulnerable system)
- HighSerious loss of integrity on the vulnerable system.
- Availability (vulnerable system)
- HighSerious loss of availability on the vulnerable system.
- Confidentiality (other systems)
- HighSerious loss of confidentiality on systems beyond the vulnerable one.
- Integrity (other systems)
- HighSerious loss of integrity on systems beyond the vulnerable one.
- Availability (other systems)
- HighSerious loss of availability on systems beyond the vulnerable one.
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. Scored by CNA (python.org).
Official description
Python has added a denylist for known compromised certificates to the "ssl" module to ensure user safety even without certificate revocation configured. Known compromised certificates will automatically be rejected regardless of the SSLContext policy configuration.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Check for Certificate Revocation
The product does not check or incorrectly checks the revocation status of a certificate.
How developers prevent this class of flaw
- Ensure that certificates are checked for revoked status.
- If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the revoked status.
More Improper Check for Certificate Revocation vulnerabilities (CWE-299)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- github.com/python/cpython/commit/21a50891ab4be2e9955239e625ae2b40c6b1854d
- github.com/python/cpython/commit/36cd295f32fc9ba19399e01abee91231440a41dd
- github.com/python/cpython/commit/48d9b2712cd52206c7a5882d0fdca4863ed65e93
- github.com/python/cpython/commit/7dd8b4736a1419750b94a388e6d158be15836fe6
- github.com/python/cpython/commit/98f0e4ed349f370dc8a00366da1a9797e11c9ed5
- github.com/python/cpython/commit/a17d9ef549008133eadf20689b1f4787902efe5b
- github.com/python/cpython/commit/af52b41afa4330fb38583db553631baa2f122f90
- github.com/python/cpython/commit/c7fd7edf7e0d122a3973cf676fae21b6aaa650a8
- github.com/python/cpython/commit/e2a9dd97ef9571c710ac0afaa834c8879aebce78
- github.com/python/cpython/commit/e4500d8a437ee5b988a5410cb9b59d177aa01370
- github.com/python/cpython/commit/e4f63e65a93cf44c14274aa987e644b8c003625e
- github.com/python/cpython/commit/e9bf2cf84eebf838a1edaa1c648c2b36345b99d3
- github.com/python/cpython/pull/160042
Other references
Other vulnerabilities in CPython
- 8.2 High severity
- 7.6 High severity
- 9.2 Critical severity
- 8.4 High severity
- 7.5 High severity
- 8.2 High severity
Recent Improper Check for Certificate Revocation vulnerabilities
- 7.4 High severity
- 8.1 High severity
- 7.4 High severity
- 8.2 High severity
- 7.4 High severity
- 8.2 High severity
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