HighCVE-2026-71889

    PKIXCertPathReviewer does not apply X.509 name constraints to the target certificate (CVE-2026-71889)

    Published Last modified Sources: Red Hat, BSI, CVE.org, SUSE

    What is affected, what to do

    A flaw was found in Bouncy Castle. The certificate path reviewer (PKIXCertPathReviewer) fails to enforce name constraints on the end-entity certificate during validation.

    Update Legion of the Bouncy Castle BC-JAVA to version 1.86, Legion of the Bouncy Castle BC-LTS-JAVA to version 2.73.13, Legion of the Bouncy Castle BC-FJA to version 1.0.13.

    Affected
    • Legion of the Bouncy Castle BC-JAVA lt *..1.86
    • Legion of the Bouncy Castle BC-LTS-JAVA lt 2.73.0..2.73.13
    • Legion of the Bouncy Castle BC-FJA lt 1.0.4..1.0.13
    • Legion of the Bouncy Castle BC-FJA lt 2.0.0..2.0.13
    • Legion of the Bouncy Castle BC-FJA lt 2.1.0..2.1.13
    Fixed in
    • Legion of the Bouncy Castle BC-JAVA 1.86
    • Legion of the Bouncy Castle BC-LTS-JAVA 2.73.13
    • Legion of the Bouncy Castle BC-FJA 1.0.13
    • Legion of the Bouncy Castle BC-FJA 2.0.13
    • Legion of the Bouncy Castle BC-FJA 2.1.13

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    Metrics

    8.7

    Priority

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

    Source: Vendor (CNA), CVSS v4

    8.7

    CVSS v4

    Severity High on the scale from 0 to 10.

    Source: Red Hat, BSI, CVE.org, SUSE

    0.2 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 5.9

    Show all metrics
    Severity
    High
    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
    73.78 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
    8.7 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
    8.7
    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“.

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    0.2 %
    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
    5.9
    Low — this CVE sits in the lower 10% of all CVEs scored today.
    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-295

    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

    A flaw was found in Bouncy Castle. The certificate path reviewer (PKIXCertPathReviewer) fails to enforce name constraints on the end-entity certificate during validation. A remote attacker can exploit this issue by presenting a certificate that violates domain restrictions imposed by an issuing Certificate Authority (CA). Applications that rely on the reviewer to determine trust may incorrectly accept unauthorized certificates as valid.

    Source: redhat_csaf, BSI WID Portal, BSI CSAF, NVD (NIST), cvelistv5, suse_csaf

    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
    Legion of the Bouncy Castle Inc.BC-FJA
    • 2.0.0 – < 2.0.13
    • 2.1.0 – < 2.1.13
    • 1.0.4 – < 1.0.13
    • 2.0.13
    • 2.1.13
    • 1.0.13
    Legion of the Bouncy Castle Inc.BC-JAVA
    • < 1.86
    • 1.86
    Legion of the Bouncy Castle Inc.BC-LTS-JAVA
    • 2.73.0 – < 2.73.13
    • 2.73.13
    Open SourceBouncy Castle Java
    • < 1.86
    • 1.86
    Open SourceBouncy Castle Java LTS
    • < 2.73.13
    • 2.73.13

    Vendors and products

    Weakness classes (CWE)

    • CWE-295Improper Certificate Validation

      Base

      The product does not validate, or incorrectly validates, a certificate.

      Entry at MITRE CWE-295

    References & sources

    • github.combcgit/bc-java/wiki/CVE‐2026‐71889Vendor advisory
    • github.combcgit/bc-java/commit/06dcff2f51037095de126986285c998e3455ab85Patch

    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 modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: yes

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2026-71889","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-05T16:55:41.462500Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. Receivedbcorg

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

      Weakness type: CWE-295

      Description added or changed

      Show 6 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      In Bouncy Castle for Java before 1.86, neither copy of PKIXCertPathReviewer - org.bouncycastle.pkix.jcajce.PKIXCertPathReviewer nor the legacy org.bouncycastle.x509.PKIXCertPathReviewer - applied X.509 name constraints to the end-entity certificate. checkNameConstraints walked the path with a loop bound of index greater than zero, which is the bound the CA-only steps require, but index zero is the target certificate under the standard CertPath ordering, so the permitted and excluded subtree checks of RFC 5280 sec. 6.1.3 (b) and (c) never ran against the leaf's subject DN or its subjectAltName. A chain whose leaf violated a NameConstraints extension imposed by its own issuing CA therefore reported isValidCertPath() true with an empty error list, while CertPathValidator.getInstance("PKIX", "BC"), which shares no code with the reviewer, rejected the identical chain against the identical trust anchor. An application using the reviewer to make the trust decision rather than for diagnostics alongside a real validation accepted a certificate the constrained CA was never authorised to issue. Both copies now check every certificate in the path including the target, waive the sec. 4.2.1.10 self-issued exemption for the final certificate as sec. 6.1.3 requires, and skip the sec. 6.1.4 (g) constraint-accumulation step for the target. This issue also affects Bouncy Castle for Java LTS before 2.73.13, which carries only the org.bouncycastle.pkix.jcajce copy of the reviewer. It also affects Bouncy Castle for Java FIPS (BC-FJA) before bcpkix-fips 1.0.13 (1.0.X series), 2.0.13 (2.0.X series) and 2.1.13 (2.1.X series).
      CVSSadded
      —
      AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/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:Amber
      Weakness type (CWE)added
      —
      CWE-295
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/71xxx/CVE-2026-71889.json">CVE-2026-71889</a>
      Referenceadded
      —
      https://github.com/bcgit/bc-java/commit/06dcff2f51037095de126986285c998e3455ab85
      Referenceadded
      —
      https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071889

      Source identifier: 91579145-5d7b-4cc5-b925-a0262ff19630

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