CriticalCVE-2026-115557

    Distrust compromised intermediate certificates in ssl module (CVE-2026-115557)

    Published Last modified Sources: pwn.watch, Msrc Update Guide, CVE.org, OSV, HKCERT

    What is affected, what to do

    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.

    Update Python Software Foundation CPython to version 3.11.18, Python Software Foundation CPython to version 3.12.16, Python Software Foundation CPython to version 3.13.18.

    Affected
    • Python Software Foundation CPython lt *..3.11.18
    • Python Software Foundation CPython lt 3.12.0..3.12.16
    • Python Software Foundation CPython lt 3.13.0..3.13.18
    • Python Software Foundation CPython lt 3.14.0..3.14.10
    • Python Software Foundation CPython lt 3.15.0..3.15.2
    • Python Software Foundation CPython lt 3.16.0a1..3.16.0
    Fixed in
    • Python Software Foundation CPython 3.11.18
    • Python Software Foundation CPython 3.12.16
    • Python Software Foundation CPython 3.13.18
    • Python Software Foundation CPython 3.14.10
    • Python Software Foundation CPython 3.15.2
    • Python Software Foundation CPython 3.16.0

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.4

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v4

    9.4

    CVSS v4

    Severity Critical on the scale from 0 to 10.

    Source: pwn.watch, Msrc Update Guide, CVE.org, OSV, HKCERT

    0.5 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 44.9

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    93.13 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.4 Methodology
    CVSS v4

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    9.4
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.5 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    44.9
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-299

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    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: pwn.watch, Microsoft Security Update Guide, cvelistv5, NVD (NIST), OSV (Open Source Vulnerabilities), CVE.org (MITRE), HKCERT (CC BY 3.0 HK) · HKCERT rating: medium

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    Python Software FoundationCPython
    • 3.12.0 – < 3.12.16
    • 3.15.0 – < 3.15.2
    • 3.16.0a1 – < 3.16.0
    • < 3.11.18
    • 3.13.0 – < 3.13.18
    • 3.14.0 – < 3.14.10
    • 3.12.16
    • 3.15.2
    • 3.16.0
    • 3.11.18
    • 3.13.18
    • 3.14.10

    Vendors and products

    Weakness classes (CWE)

    • CWE-299Improper Check for Certificate Revocation

      Base

      The product does not check or incorrectly checks the revocation status of a certificate, which may cause it to use a certificate that has been compromised.

      Entry at MITRE CWE-299

    References & sources

    • pwn.watchpwn.watch: eMudhra intermediate CA private keys compromisedpwn-watch
    • blog.googleProtecting Chrome and Android Users from Compromised eMudhra Intermediate CA Certificatespwn-watch
    • bugzilla.mozilla.orgBug 2083449 - eMudhra: Private key compromise of Intermediate Certificatespwn-watch
    • news.ycombinator.comeMudhra ignored Mozilla Root investigation deadline; blames social mediapwn-watch
    • github.comElectron GHSA-jr5w-w6x2-84p9 (CVE-2026-115570): Mitigation for compromised eMudhra intermediate certificates (fixed in 45.0.0-beta.6, 44.9.1, 43.8.1, 42.11.16)pwn-watch
    • graalvm.orgeMudhra certificate compromise: GraalVM Native Image advisorypwn-watch
    • ftp.openbsd.orgLibreSSL 4.3.4 release notes: eMudhra emSign ECC Root CA - G3 removed from cert.pempwn-watch
    • openbsd.orgOpenBSD 8.0 errata 005: dbupdate utility and updated /etc/ssl/cert.pempwn-watch
    • thedefiant.ioLightning Labs Urges Immediate Updates Over Certificate Vulnerabilitypwn-watch
    • thehackernews.comeMudhra to Exit Global SSL/TLS Business After 8 Intermediate CA Keys Found Easily Guessablepwn-watch
    • emudhra.we-have-a-problem.comeMudhra Intermediate CA Compromise trackerpwn-watch, Third-party advisory, web
    • discuss.python.orgInformation for Python users regarding eMudhra / emSign CA certificate security incidentpwn-watch
    • advisories.gitlab.comGHSA-6q48-6c7w-9gw2: certifi bundles emSign root CAs with compromised intermediate CA keyspwn-watch
    • pip.pypa.iopip 26.2.2 changelog (upgrade certifi to 2026.10.19)pwn-watch
    • github.comuv 0.13.4 release (GHSA-hq85-5cpj-mr62)pwn-watch
    • emudhra.comeMudhra statement on certificate security incidentpwn-watch
    • bleepingcomputer.comMozilla, Google, Apple block compromised eMudhra CA certificatespwn-watch
    • openjdk.orgOpenJDK Vulnerability Advisory: 2026/10/21 (CVE-2026-91403)pwn-watch
    • oracle.comOracle Security Alert Advisory - CVE-2026-91403pwn-watch
    • blog.cloudflare.comeMudhra certificate compromisepwn-watch

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedpython.org

      1 individual change: Affected versions (publisher)

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/115xxx/CVE-2026-115557.json">CVE-2026-115557</a>

      Source identifier: cna@python.org

    2. Record modifiedpython.org

      1 individual change: Affected versions (publisher)

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/115xxx/CVE-2026-115557.json">CVE-2026-115557</a>

      Source identifier: cna@python.org

    3. Record modifiedpython.org

      Show 13 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/115xxx/CVE-2026-115557.json">CVE-2026-115557</a>
      Referenceadded
      —
      https://github.com/python/cpython/commit/21a50891ab4be2e9955239e625ae2b40c6b1854d
      Referenceadded
      —
      https://github.com/python/cpython/commit/36cd295f32fc9ba19399e01abee91231440a41dd
      Referenceadded
      —
      https://github.com/python/cpython/commit/48d9b2712cd52206c7a5882d0fdca4863ed65e93
      Referenceadded
      —
      https://github.com/python/cpython/commit/7dd8b4736a1419750b94a388e6d158be15836fe6
      Referenceadded
      —
      https://github.com/python/cpython/commit/98f0e4ed349f370dc8a00366da1a9797e11c9ed5
      Referenceadded
      —
      https://github.com/python/cpython/commit/a17d9ef549008133eadf20689b1f4787902efe5b
      Referenceadded
      —
      https://github.com/python/cpython/commit/af52b41afa4330fb38583db553631baa2f122f90
      Referenceadded
      —
      https://github.com/python/cpython/commit/c7fd7edf7e0d122a3973cf676fae21b6aaa650a8
      Referenceadded
      —
      https://github.com/python/cpython/commit/e2a9dd97ef9571c710ac0afaa834c8879aebce78
      Referenceadded
      —
      https://github.com/python/cpython/commit/e4500d8a437ee5b988a5410cb9b59d177aa01370
      Referenceadded
      —
      https://github.com/python/cpython/commit/e4f63e65a93cf44c14274aa987e644b8c003625e
      Referenceadded
      —
      https://github.com/python/cpython/commit/e9bf2cf84eebf838a1edaa1c648c2b36345b99d3

      Source identifier: cna@python.org

    4. Record modifiedCVE Program

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      http://www.openwall.com/lists/oss-security/2026/10/24/5

      Source identifier: af854a3a-2127-422b-91ae-364da2661108

    5. Receivedpython.org

      CVSS V4.0: AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

      Weakness type: CWE-299

      Description added or changed

      Show 9 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      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.
      CVSSadded
      —
      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
      Weakness type (CWE)added
      —
      CWE-299
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/115xxx/CVE-2026-115557.json">CVE-2026-115557</a>
      Referenceadded
      —
      http://www.openwall.com/lists/oss-security/2026/10/20/29
      Referenceadded
      —
      https://emudhra.we-have-a-problem.com/
      Referenceadded
      —
      https://github.com/python/cpython/issues/160040
      Referenceadded
      —
      https://github.com/python/cpython/pull/160042
      Referenceadded
      —
      https://mail.python.org/archives/list/security-announce@python.org/thread/FNAJMZV6XQYLVPABNINDMF3VF66AYLW4/

      Source identifier: cna@python.org

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