CVE-2026-17507 (GCVE-0-2026-17507)

Vulnerability from cvelistv5 – Published: 2026-10-02 07:26 – Updated: 2026-10-02 17:43
VLAI
Title
MLS membership checks compare a uint32 leaf_index as signed, admitting an out-of-range sender
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.
Severity
8.7 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/U:Amber
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-02 17:43 UTC
CWE
  • CWE-195 - Signed to Unsigned Conversion Error
Assigner
References
Impacted products
Vendor Product Version CPE status
Legion of the Bouncy Castle Inc. BC-JAVA Affected: 1.73 , < 1.86 (maven)
guessed Create a notification for this product.
Credits
Mirko Swillus on behalf of Alpha-Omega (alpha-omega.dev), using Scrutineer with an Anthropic Claude model provided through Project Glasswing
Show details on NVD website
To clipboard 

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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.