CVE-2026-71890

Bouncy Castle for Java versions before 1.86 are vulnerable to an authorization flaw in the MLS (RFC 9420) protocol implementation. The org.bouncycastle.mls.protocol.Group.validateExternalCachedProposals method fails to verify that a Remove proposal in an external commit belongs to the joiner. Thi...

CVE-2026-71890 MLS external commit can remove an arbitrary group member

In Bouncy Castle for Java before 1.86, validation of an MLS RFC 9420 external commit's proposal list, org.bouncycastle.mls.protocol.Group.validateExternalCachedProposals, counted the proposals by type and bounded the removed leaf index but never established that the removed leaf had anything to d...

CVE-2026-71890 MLS external commit can remove an arbitrary group member

In Bouncy Castle for Java before 1.86, validation of an MLS RFC 9420 external commit's proposal list, org.bouncycastle.mls.protocol.Group.validateExternalCachedProposals, counted the proposals by type and bounded the removed leaf index but never established that the removed leaf had anything to d...