Threats affecting pkg:maven/Legion of the Bouncy Castle Inc./bcmls

CVE-2026-71890 is a high-severity authorization vulnerability in Bouncy Castle for Java (BC-JAVA) versions from 1.73 up to but not including 1.86. The flaw involves improper validation of MLS external commit proposal lists, allowing an external joiner to remove any group member and take over their slot in the ratchet tree. This occurs because the validation did not ensure the removed leaf corresponded to the joiner, violating RFC 9420 requirements. The issue was fixed in version 1.86 by enforcing credential checks on both sending and receiving sides.

CVE-2026-71885 is a critical vulnerability in Bouncy Castle for Java (BC-JAVA) versions before 1.86 affecting the Messaging Layer Security (MLS) implementation. The flaw involves improper certificate validation where the X.509 certificate chain is not properly bound to the LeafNode's signature key, allowing an attacker to impersonate another party's identity within a group. This can lead to unauthorized admission, eviction of legitimate members, and decryption and injection of group messages. The issue is fixed in version 1.86 by enforcing that the end-entity certificate's public key matches the signature key as required by RFC 9420. Deployments using only basic credentials are not affected.

In Bouncy Castle for Java before 1.85, MLS wire decoder allocates attacker-declared opaque length before bounds check.