Improper Certificate Validation Affecting org.bouncycastle:bcmls-jdk18on package, versions [,1.86)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JAVA-ORGBOUNCYCASTLE-20416734
- published4 Oct 2026
- disclosed3 Oct 2026
- creditJoshua Rogers, Khaled Suliman
Introduced: 3 Oct 2026
NewCVE-2026-71885 (opens in a new tab)How to fix?
Upgrade org.bouncycastle:bcmls-jdk18on to version 1.86 or higher.
Overview
Affected versions of this package are vulnerable to Improper Certificate Validation in LeafNode.verify() in org.bouncycastle.mls.codec, which never checks that the subject public key of the X.509 credential's end entity certificate matches the leaf's signature_key field, although RFC 9420 section 5.3 requires the two to represent the same identity. An attacker can be admitted to an MLS group under a victim's X.509 identity and decrypt the group messages that follow, by presenting the victim's certificate as their credential while signing the leaf with an unrelated key they control. This affects applications using the MLS implementation, with no second check available, since both KeyPackage.verify() and the Group leaf validation path authenticate through that same method, and validating the certificate chain to a trust anchor is a separate concern that the application handles and that does not establish this binding.