{"answers":{"affected":"","exploited":"There is no known exploitation of CVE-2026-71891 in the wild and no public exploit code.","fix":"Upgrade to a fixed version.","what":"CVE-2026-71891 is a high-severity 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, and only if a user opens a file or follows a link."},"fix_prompt":"Check this codebase for CVE-2026-71891 and fix it if it is affected.\n\nWhat it is: CVE-2026-71891 is a high-severity 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, and only if a user opens a file or follows a link.\nExploitation: There is no known exploitation of CVE-2026-71891 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-2026-71891/ (Markdown: https://insights.sbomify.com/CVE-2026-71891/index.md)","id":"CVE-2026-71891","markdown":"https://insights.sbomify.com/CVE-2026-71891/index.md","name":"CVE-2026-71891","record":{"aliases":["CLEANSTART-2026-DK36206","CLEANSTART-2026-HW07490","CLEANSTART-2026-KF30791","DEBIAN-CVE-2026-71891","GHSA-gggh-4cvh-v637","UBUNTU-CVE-2026-71891"],"analysis":{"component_type":"library","fix_type":"upgrade","impacts":["security_bypass"],"network_reachable":"yes","non_default_config":true,"product_category":"Java cryptography library","requires_auth":"none","summary":"Attackers can bypass BLS12-381 signature verification by using a public key from a foreign curve, allowing phantom signers in aggregate signatures.","user_interaction":"required","vuln_class":"security_feature_bypass"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"bcorg","cpe":[],"cvss":{"score":7.1,"severity":"high","source":"cna","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/U:Amber","version":"4.0"},"cwes":[{"id":"CWE-347","name":"Improper Verification of Cryptographic Signature"}],"description":"In Bouncy Castle for Java before 1.86, BLS12_381BasicScheme.keyValidate, and so BLSPublicKeyParameters and every BasicScheme, MessageAugmentation and ProofOfPossession verify and aggregateVerify that gate on it, accepted a public key built on a foreign ECCurve that merely shares BLS12-381's field characteristic. The prime-order subgroup check trusts a point's own curve to name its cofactor, since ECPoint.satisfiesOrder returns true outright when the curve's cofactor is one, so a point on a curve with a different equation and a cofactor forged to one passed keyValidate despite not being a G1 point at all. In BC's pairing implementation such a point contributes the identity in the target group, so an aggregate signature verified against a set of public keys including it is accepted even though it contains no signature for that key and message pair, admitting a phantom signer. keyValidate now first confirms that the point's curve carries exactly the canonical G1 field, equation, order and cofactor before any subgroup check. The issue is reachable only where an application constructs an ECPoint on an explicit, non-canonical curve and accepts it as an authority-bearing key; the standard 48-byte compressed-point decoder always supplies the canonical curve and was never affected.","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":"BLS12-381 key validation accepts a public key built on a foreign curve","id":"CVE-2026-71891","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":null,"product":null,"products":[],"type":"security_feature_bypass","year":"2026"},"n_packages":0,"n_references":2,"next":{"headline":"CMS key-transport recipient key-size validation never runs for RFC 9709 HKDF-derived keys","id":"CVE-2026-71892"},"packages":[],"prev":{"headline":"MLS external commit can remove an arbitrary group member","id":"CVE-2026-71890"},"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":"no","exploitation":"none","technical_impact":"partial"},"state":"PUBLISHED","updated":"2026-10-05","vendors":["Legion of the Bouncy Castle Inc."]},"summary":"Attackers can bypass BLS12-381 signature verification by using a public key from a foreign curve, allowing phantom signers in aggregate signatures.","url":"https://insights.sbomify.com/CVE-2026-71891/"}