CVE-2026-115557

Distrust compromised intermediate certificates in ssl module

Published Oct 24, 2026 CVSS 4.0 · 9.4 Critical EPSS < 1% KEV · Not listed

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.

Analysis

Technical impact

Python's ssl module previously accepted any certificate chain unless explicit revocation was configured. This oversight allowed attackers to use compromised intermediate certificates to create seemingly valid TLS connections, enabling eavesdropping or credential theft. The issue is classified as a Trust Management flaw (CWE‑299) and carries a high severity of CVSS 9.4, indicating a serious threat to confidentiality and integrity.

Affected Systems

The flaw affects the Python Software Foundation's CPython implementation. All CPython releases prior to the fix that do not contain the denylist for known compromised certificates are vulnerable, regardless of operating system or platform.

Risk and Exploitability

The vulnerability can be exploited during the SSL/TLS handshake when a client accepts a server certificate chain that includes a compromised intermediate. Attackers who control the intermediate can impersonate legitimate servers. The EPSS score is not available, but the high CVSS score and absence from the KEV catalog mean the risk remains significant unless mitigated with the official patch.

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Python Software Foundation

CPython

unaffected

Version	Status	Constraints
`0`	affected	< 3.11.18
`3.12.0`	affected	< 3.12.16
`3.13.0`	affected	< 3.13.18
`3.14.0`	affected	< 3.14.10
`3.15.0`	affected	< 3.15.2
`3.16.0a1`	affected	< 3.16.0

No data.

Vendor Product Versions

Python

Cpython

Version	Status	Scheme	Platform
`[0,3.16.0]`	affected	generic	—

Python Software Foundation

Cpython

Version	Status	Scheme	Platform
`[0,3.16.0]`	affected	generic	—

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Upgrade to a CPython release that contains the denylist for compromised certificates.
Configure your Python applications to enforce strict SSL/TLS certificate verification, ensuring that any certificate chain is validated against a trusted certificate authority and rejecting chains that include compromised intermediates.
If the patch cannot be applied immediately, modify your application to perform an additional check against the known compromised certificate list (e.g., by adding logic that examines the issuer field of intermediate certificates and rejects the connection if it matches an entry in the denylist).

Generated by OpenCVE AI on October 24, 2026 at 15:50 UTC.

Tracking

Advisories

No advisories available

Metrics

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction Passive

Vulnerable System Confidentiality Impact High

Vulnerable System Integrity Impact High

Vulnerable System Availability Impact High

Subsequent System Confidentiality Impact High

Subsequent System Integrity Impact High

Subsequent System Availability Impact High

No CVSS v3.1

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.534% probability within 30 days)

Exploitation none

Automatable no

Technical Impact total

References

Link	Providers
http://www.openwall.com/lists/oss-security/2026/10/20/29
http://www.openwall.com/lists/oss-security/2026/10/24/5
https://emudhra.we-have-a-problem.com/
https://github.com/python/cpython/commit/21a50891ab4be2e9955239e625ae2b40c6b1854d
https://github.com/python/cpython/commit/36cd295f32fc9ba19399e01abee91231440a41dd
https://github.com/python/cpython/commit/48d9b2712cd52206c7a5882d0fdca4863ed65e93
https://github.com/python/cpython/commit/7dd8b4736a1419750b94a388e6d158be15836fe6
https://github.com/python/cpython/commit/98f0e4ed349f370dc8a00366da1a9797e11c9ed5
https://github.com/python/cpython/commit/a17d9ef549008133eadf20689b1f4787902efe5b
https://github.com/python/cpython/commit/af52b41afa4330fb38583db553631baa2f122f90
https://github.com/python/cpython/commit/c7fd7edf7e0d122a3973cf676fae21b6aaa650a8
https://github.com/python/cpython/commit/e2a9dd97ef9571c710ac0afaa834c8879aebce78
https://github.com/python/cpython/commit/e4500d8a437ee5b988a5410cb9b59d177aa01370
https://github.com/python/cpython/commit/e4f63e65a93cf44c14274aa987e644b8c003625e
https://github.com/python/cpython/commit/e9bf2cf84eebf838a1edaa1c648c2b36345b99d3
https://github.com/python/cpython/issues/160040
https://github.com/python/cpython/pull/160042
https://mail.python.org/archives/list/security-announce@python.org/thread/FNAJMZV6XQYLVPABNINDMF3VF66AYLW4/

History

Nov 2, 2026 3:30 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}`

Oct 25, 2026 1:15 AM Added references View changes

Type	Values Removed	Values Added
References		https://github.com/python/cpython/commit/21a50891ab4be2e9955239e625ae2b40c6b1854d https://github.com/python/cpython/commit/36cd295f32fc9ba19399e01abee91231440a41dd https://github.com/python/cpython/commit/48d9b2712cd52206c7a5882d0fdca4863ed65e93 https://github.com/python/cpython/commit/7dd8b4736a1419750b94a388e6d158be15836fe6 https://github.com/python/cpython/commit/98f0e4ed349f370dc8a00366da1a9797e11c9ed5 https://github.com/python/cpython/commit/a17d9ef549008133eadf20689b1f4787902efe5b https://github.com/python/cpython/commit/af52b41afa4330fb38583db553631baa2f122f90 https://github.com/python/cpython/commit/c7fd7edf7e0d122a3973cf676fae21b6aaa650a8 https://github.com/python/cpython/commit/e2a9dd97ef9571c710ac0afaa834c8879aebce78 https://github.com/python/cpython/commit/e4500d8a437ee5b988a5410cb9b59d177aa01370 https://github.com/python/cpython/commit/e4f63e65a93cf44c14274aa987e644b8c003625e https://github.com/python/cpython/commit/e9bf2cf84eebf838a1edaa1c648c2b36345b99d3

Oct 24, 2026 6:30 PM Added references View changes

Type	Values Removed	Values Added
References		http://www.openwall.com/lists/oss-security/2026/10/24/5

Oct 24, 2026 4:00 PM First appearance in the feed. Affected vendors updated View changes

Type	Values Removed	Values Added
First Time appeared		Python Python cpython Python Software Foundation Python Software Foundation cpython
Vendors & Products		Python Python cpython Python Software Foundation Python Software Foundation cpython

Oct 24, 2026 2:30 PM Description updated. Title updated. Weaknesses updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
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.
Title		Distrust compromised intermediate certificates in ssl module
Weaknesses		CWE-299
References		http://www.openwall.com/lists/oss-security/2026/10/20/29 https://emudhra.we-have-a-problem.com/ https://github.com/python/cpython/issues/160040 https://github.com/python/cpython/pull/160042 https://mail.python.org/archives/list/security-announce@python.org/thread/FNAJMZV6XQYLVPABNINDMF3VF66AYLW4/
Metrics		cvssV4_0 `{'score': 9.4, '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'}`