CVE Intelligence
Critical

CVE-2026-115557 — Distrust compromised intermediate certificates in ssl module

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.

Published Oct 24, 2026 · Updated Oct 26, 2026 · Sources: CVE Program (cve.org) e CISA ADP, NIST National Vulnerability Database, GitHub Security Advisories · CNA: PSF

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.5% (30-day exploitation probability)+7
  • Technical severity (critical)+10

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.53%
ahead of 45% of scored CVEs · Oct 28, 2026
Affects
Python
CPython
CVSS base
9.4
Critical · 2 source(s)

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Python CPython).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  4. Exploitation requires user interaction: tighten email/web filtering and warn affected users.
  5. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Python CPython < 3.11.18≥ 3.12.0 and < 3.12.16≥ 3.13.0 and < 3.13.18≥ 3.14.0 and < 3.14.10≥ 3.15.0 and < 3.15.2≥ 3.16.0a1 and < 3.16.0 Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Attack requirements
None
Privileges required
None
User interaction
Passive
Scope
X
Confidentiality (vulnerable system)
High
Integrity (vulnerable system)
High
Availability (vulnerable system)
High
Confidentiality (subsequent)
High
Integrity (subsequent)
High
Availability (subsequent)
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
9.4 CVSS 4.0 Critical — — cna@python.org via NIST National Vulnerability Database
9.4 CVSS 4.0 Critical — — PSF via CVE Program (cve.org) e CISA ADP
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 (score shown at the top: cna@python.org)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-299

Other CVEs with this weakness →

EPSS over time FIRST

Oct 25, 2026 → Oct 28, 2026 · 4 reading(s) · max 0.53%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products removed · 1
    Oct 26, 2026 · CVE Program (cve.org) e CISA ADP
  • Affected products added · python software foundation/cpython
    Oct 26, 2026 · CVE Program (cve.org) e CISA ADP
  • Source status changed · Received → Awaiting Analysis
    Oct 26, 2026 · NIST National Vulnerability Database
  • Affected products removed · 1
    Oct 25, 2026 · CVE Program (cve.org) e CISA ADP
  • Affected products added · python software foundation/cpython
    Oct 25, 2026 · CVE Program (cve.org) e CISA ADP
  • Affected products removed · 1
    Oct 24, 2026 · CVE Program (cve.org) e CISA ADP
  • Affected products added · python software foundation/cpython
    Oct 24, 2026 · CVE Program (cve.org) e CISA ADP
  • Source status changed · Published → Received
    Oct 24, 2026 · NIST National Vulnerability Database
  • Record published
    Oct 24, 2026
  • CVSS changed · 9.4
    Oct 24, 2026 · CVE Program (cve.org) e CISA ADP
  • Source status changed · → Published
    Oct 24, 2026 · CVE Program (cve.org) e CISA ADP
  • Record created in this database
    Oct 24, 2026 · CVE Program (cve.org) e CISA ADP
  • CVE published
    Oct 24, 2026 · PSF

Source activity

Repeated readings are counted rather than listed.

  • 3× References added · Oct 24, 2026 – Oct 24, 2026
  • 1× Official description updated · Oct 24, 2026 – Oct 24, 2026

References

22 on the record

Elsewhere on this site

Python
every CVE for this vendor
CWE-299
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-103995 Lenient parsing of integers for response body and chunk framing 1d
  • CVE-2026-114583 tar filter allows writing outside destination via empty-named symlink 6d
  • CVE-2026-19553 SSLContext.wrap_bio() missing validation of server_hostname parameter 28d
  • CVE-2026-19445 Use-after-free of a server-side SSLContext when sni_callback switches contexts 28d
  • CVE-2026-12345 Race condition in tempfile.TemporaryDirectory cleanup allows deleting files outside the temporary directory 29d
  • CVE-2026-82049 tarfile extraction filters allow file modification and content disclosure via hard link to symlink Sep 14, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No fixed version, patch or mitigation documented.
  • No CISA SSVC assessment.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-115557 is "Distrust compromised intermediate certificates in ssl module", rated Critical. It affects CPython (Python); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 9.4 describes technical severity. EPSS 0.53% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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