MLS membership checks compare a uint32 leaf_index as signed, admitting an out-of-range sender
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- Fix
- Fixed in 1.86
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: yes
- Technical impact: partial
Summary
In Bouncy Castle for Java before 1.86, the MLS implementation (org.bouncycastle.mls) holds RFC 9420's uint32 leaf_index in a signed int, so a wire value with the top bit set decodes to a negative number. That is a legitimate encoding rather than malformed input, and it must still decode, since the MLS interop test vectors round-trip the full range. GroupKeySet.SecretTree.hasLeaf and Group.validateRemove compared the decoded value directly against the tree's leaf count, and a signed comparison treats any negative int as less than a positive bound, so an out-of-range sender passed the membership check. In the hasLeaf case the SenderData of an unprotected PrivateMessage could then drive LeafIndex.directPath through NodeIndex.parent() arithmetic that never reaches the tree root, growing the resulting node list without bound until the JVM exhausted its heap. A single small message from any current group member could therefore deny service to every other member of the group. Both comparisons now interpret the value as unsigned via Integer.toUnsignedLong, rejecting an out-of-range sender however it was encoded; well-formed leaf indices are unaffected.
Timeline
- CVE published
- CISA SSVC assessment
Exploitation: none · Automatable: yes · Technical impact: partial
- Record last updated
Affected versions
- bcmls
From 1.73 · fixed in 1.86