{"answers":{"affected":"","exploited":"There is no known exploitation of CVE-2026-71890 in the wild and no public exploit code.","fix":"Upgrade to a fixed version.","what":"CVE-2026-71890 is a high-severity missing authorization vulnerability in Legion of the Bouncy Castle Inc. BC-JAVA, published on 3 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim."},"fix_prompt":"Check this codebase for CVE-2026-71890 and fix it if it is affected.\n\nWhat it is: CVE-2026-71890 is a high-severity missing authorization vulnerability in Legion of the Bouncy Castle Inc. BC-JAVA, published on 3 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.\nExploitation: There is no known exploitation of CVE-2026-71890 in the wild and no public exploit code.\n\nAffected product: Legion of the Bouncy Castle Inc. BC-JAVA. No package-level version data is available, so check the vendor advisory linked from the reference page.\n\nTask:\n1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.\n2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.\n3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.\n4. Run the tests and summarise what changed and why.\n5. If nothing in the project is affected, say so and change nothing.\n\nReference: https://insights.sbomify.com/CVE-2026-71890/ (Markdown: https://insights.sbomify.com/CVE-2026-71890/index.md)","id":"CVE-2026-71890","markdown":"https://insights.sbomify.com/CVE-2026-71890/index.md","name":"CVE-2026-71890","record":{"aliases":["CLEANSTART-2026-YZ86171","DEBIAN-CVE-2026-71890","GHSA-jc55-7frr-fv5r","UBUNTU-CVE-2026-71890"],"analysis":{"component_type":"library","fix_type":"upgrade","impacts":["privilege_escalation","data_modify"],"network_reachable":"yes","non_default_config":false,"product_category":"Java cryptography library","requires_auth":"none","summary":"An attacker with group info can evict any member and take their slot in the MLS ratchet tree due to missing credential validation in external commits.","user_interaction":"not_required","vuln_class":"missing_authorization"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"bcorg","cpe":[],"cvss":{"score":8.7,"severity":"high","source":"cna","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/U:Amber","version":"4.0"},"cwes":[{"id":"CWE-863","name":"Incorrect Authorization"}],"description":"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 do with the joiner. RFC 9420 sec. 12.2 permits at most one Remove proposal in an external commit, with which the joiner removes an old version of themselves, and requires that where one is present the LeafNode in the commit's path field meet the criteria it would have to meet in an Update for the removed leaf, in particular that its credential present identifiers acceptable for the removed participant. The ordinary proposal-list validator's self-remove rule is deliberately not applied on this path, because a resync commit legitimately removes a leaf the joiner owns, but nothing was put in its place. Any party holding the group's public GroupInfo, which is precisely what an external joiner is meant to be given, could therefore commit a Remove naming any member's LeafIndex and have every member apply it, evicting that member and taking over their slot in the ratchet tree. The credential check that should have prevented this existed only in the gRPC interop harness and so protected no other caller of the public Group.externalJoin and Group.handle API. An external commit carrying a Remove is now accepted only when the removed leaf's credential is identical to the one in the joiner's own new leaf, on both the sending and the receiving side.","ecosystems":[],"exploits":{"exploitdb":0,"first_seen":null,"github_poc":0,"max_poc_stars":null,"metasploit":0,"nuclei":0,"refs":[],"tier":"none_known"},"has_fix":true,"headline":"MLS external commit can remove an arbitrary group member","id":"CVE-2026-71890","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":null,"product":null,"products":[],"type":"missing_authorization","year":"2026"},"n_packages":0,"n_references":2,"next":{"headline":"BLS12-381 key validation accepts a public key built on a foreign curve","id":"CVE-2026-71891"},"packages":[],"prev":{"headline":"PKIXCertPathReviewer does not apply X.509 name constraints to the target certificate","id":"CVE-2026-71889"},"products":["BC-JAVA"],"published":"2026-10-03","related":[],"sources":[{"class":"attribution","licence":"CVE Terms of Use (MITRE)","name":"CVE List","prefix":"CVE"},{"class":"attribution","licence":"CWE Terms of Use","name":"CWE (MITRE)"},{"class":"attribution","licence":"FIRST CVSS licence","name":"CVSS (FIRST)"}],"ssvc":{"automatable":"yes","exploitation":"none","technical_impact":"partial"},"state":"PUBLISHED","updated":"2026-10-05","vendors":["Legion of the Bouncy Castle Inc."]},"summary":"An attacker with group info can evict any member and take their slot in the MLS ratchet tree due to missing credential validation in external commits.","url":"https://insights.sbomify.com/CVE-2026-71890/"}