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

Quick assessment

Affected
Legion of the Bouncy Castle Inc. BC-JAVA
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 Bouncy Castle for Java 1.86 版本之前的产品中，PKIXCertPathReviewer 的两个副本（即 和传统的 ）均未对终Entity 证书（end-entity certificate，即叶证书）应用 X.509 名称约束（Name Constraints）。 具体问题在于： 方法在遍历证书链时，使用了循环索引大于零的上界。这一设置符合仅由证书颁发机构（CA）证书执行步骤的要求，但在标准的证书路径（CertPath）顺序中，索引为零对应的是目标证书（即叶证书）。因此，RFC 52

CVSS 8.7 · High EPSS 0.17% · P5

Possible ATT&CK Techniques 1 AI

T1557 · Adversary-in-the-Middle

Affected Version Matrix 6

VendorProduct Version RangeStatus
Legion of the Bouncy Castle Inc. BC-FJA 1.0.4< 1.0.13 affected
2.0.0< 2.0.13 affected
2.1.0< 2.1.13 affected
Legion of the Bouncy Castle Inc. BC-JAVA < 1.86 affected
< 1.86 affected
Legion of the Bouncy Castle Inc. BC-LTS-JAVA 2.73.0< 2.73.13 affected
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I. Basic Information for CVE-2026-71889

Vulnerability Information
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Vulnerability Title
PKIXCertPathReviewer does not apply X.509 name constraints to the target certificate
Source: CVE Program / CVE List V5
Vulnerability Description
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).
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/U:Amber
Source: CVE Program / CVE List V5
Vulnerability Type
证书验证不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Legion of the Bouncy Castle Inc. BC-JAVA 0 ~ 1.86 -
Legion of the Bouncy Castle Inc. BC-JAVA 0 ~ 1.86 -
Legion of the Bouncy Castle Inc. BC-LTS-JAVA 2.73.0 ~ 2.73.13 -
Legion of the Bouncy Castle Inc. BC-FJA 1.0.4 ~ 1.0.13 -

II. Public POCs for CVE-2026-71889

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III. Intelligence Information for CVE-2026-71889

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Patches & Fixes for CVE-2026-71889 (1)

News Coverage for CVE-2026-71889 (1)

Same Patch Batch · Legion of the Bouncy Castle Inc. · 2026-10-03 · 12 CVEs total

CVE-2026-71885 9.2 CRITICAL MLS X.509 credential not bound to the LeafNode signature key
CVE-2026-71888 8.7 HIGH CMS AuthenticatedData exposes attacker-inserted authAttrs when digestAlgorithm is absent
CVE-2026-71890 8.7 HIGH MLS external commit can remove an arbitrary group member
CVE-2026-85515 8.2 HIGH OpenPGP message truncation not reported, bypassing the SEIPDv1 integrity check
CVE-2026-71887 8.2 HIGH OpenPGP data signature accepted from a signing subkey without cross-certification
CVE-2026-71883 8.2 HIGH Native AES packet cipher returns the raw AES key on an alias
CVE-2026-71886 8.2 HIGH OpenPGP certification accepted from a subkey without certification authority
CVE-2026-71891 7.1 HIGH BLS12-381 key validation accepts a public key built on a foreign curve
CVE-2026-71892 6.9 MEDIUM CMS key-transport recipient key-size validation never runs for RFC 9709 HKDF-derived keys
CVE-2026-18040 5.9 MEDIUM HQC leaks private key information through secret-indexed GF(2^8) tables and a secret-depen
CVE-2026-97873 5.3 MEDIUM Legacy PBES1 and PKCS#12 PBE iteration count honoured unbounded in the raw JCA provider

IV. Related Vulnerabilities

Same product: BC-JAVA
Same vendor: Legion of the Bouncy Castle Inc.
Same weakness: CWE-295

V. Comments for CVE-2026-71889

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