CVE-2026-71885— MLS X.509凭证未绑定到LeafNode签名密钥
一分钟漏洞结论
影响对象
Legion of the Bouncy Castle Inc. BC-JAVA
利用判断
尚无明确在野利用证据，仍需结合暴露面评估
建议动作
优先检查厂商安全公告和参考链接中的修复版本；无法立即升级时，限制受影响服务暴露并加强监测。
在 Java 版 Bouncy Castle 1.86 之前的版本中，消息层安全（MLS，RFC 9420）的实现未将 X.509 证书凭据与 LeafNode 的 signature_key（签名密钥）进行绑定。LeafNode.verify() 方法仅检查叶节点自身的签名是否与其携带的 signature_key 匹配；而证书链中的 X.509 证书虽然被存储，但从未被解析或验证。因此，最终实体证书的公钥无需与 signature_key 匹配，这不符合 RFC 9420 第 5.3 节的要求。 攻击者因此可以
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一、 漏洞 CVE-2026-71885 基础信息
漏洞信息
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Vulnerability Title
MLS X.509 credential not bound to the LeafNode signature key
来源: CVE Program / CVE List V5
Vulnerability Description
In Bouncy Castle for Java before 1.86, the Messaging Layer Security (MLS, RFC 9420) implementation did not bind an X.509 credential to a LeafNode's signature_key. LeafNode.verify() checked a leaf's signature against the signature_key carried in the leaf itself, while the credential's X.509 certificate chain was stored but never parsed or validated, so the end-entity certificate's public key was never required to match signature_key as RFC 9420 sec. 5.3 requires. A party could therefore present another party's certificate as its credential while signing the leaf, and the enclosing KeyPackage, with an unrelated key, and be accepted under that other party's identity through KeyPackage.verify() and the Group leaf-validation path. In a deployment that admits external commits without an independent credential-admission check, an unauthenticated attacker could be admitted under a victim's X.509 identity, evict the victim (resynchronization compares whole credentials rather than signing keys), derive the current epoch, decrypt subsequent group messages, and send messages accepted as the victim. TreeKEM.LeafNode now requires the end-entity certificate's subject public key, in the cipher suite's signature encoding, to equal signature_key for an X.509 credential and rejects the leaf otherwise, including an empty chain or a certificate whose key type does not match the cipher suite; certificate-chain and identity validation to a trust anchor remain the application's responsibility per RFC 9420 sec. 5.3.1. Deployments using only basic credentials are unaffected.
来源: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/U:Amber
来源: CVE Program / CVE List V5
Vulnerability Type
证书验证不恰当
来源: CVE Program / CVE List V5
受影响产品
| 厂商 | 产品 | 影响版本 | CPE | 订阅 |
|---|---|---|---|---|
| Legion of the Bouncy Castle Inc. | BC-JAVA | 0 ~ 1.86 | - |
|
二、漏洞 CVE-2026-71885 的公开POC
| # | POC 描述 | 源链接 | 神龙链接 |
|---|
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CVE-2026-71885 其他参考 (2)
同批安全公告 · Legion of the Bouncy Castle Inc. · 2026-10-03 · 共 12 条
| CVE-2026-71888 | 8.7 HIGH | CMS 认证数据暴露攻击者插入的authAttrs |
| CVE-2026-71889 | 8.7 HIGH | PKIXCertPathReviewer X.509名称约束绕过漏洞 |
| CVE-2026-71890 | 8.7 HIGH | MLS外部提交可移除任意组成员漏洞 |
| CVE-2026-85515 | 8.2 HIGH | OpenPGP消息截断未报告，绕过SEIPDv1完整性检查 |
| CVE-2026-71887 | 8.2 HIGH | OpenPGP 签名子键无交叉认证漏洞 |
| CVE-2026-71883 | 8.2 HIGH | Native AES密文解析器泄露原始AES密钥 |
| CVE-2026-71886 | 8.2 HIGH | OpenPGP 子键无证书认证漏洞 |
| CVE-2026-71891 | 7.1 HIGH | BLS12-381 密钥验证接受基于外部曲线的公钥 |
| CVE-2026-71892 | 6.9 MEDIUM | RFC 9709 HKDF派生密钥未执行CMS密钥传输接收方密钥大小验证 |
| CVE-2026-18040 | 5.9 MEDIUM | HQC 通过秘密索引表和采样器泄露私钥信息 |
| CVE-2026-97873 | 5.3 MEDIUM | JCA原始提供程序未限制PBES1和PKCS#12迭代次数 |
IV. Related Vulnerabilities
V. Comments for CVE-2026-71885
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