Bouncy Castle is a widely used Java crypto library; this flaw enables identity spoofing and group decryption across apps using MLS with X.509, impacting many enterprise deployments.
CVE-2026-71885
MLS X.509 binding flaw in Bouncy Castle allows identity spoofing and group decryption
Is CVE-2026-71885 being exploited?
Not confirmed. CVE-2026-71885 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked.
How severe is CVE-2026-71885?
CVE-2026-71885 is rated Critical with a CVSS score of 9.2. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-71885?
Yes. A fix has been recorded for CVE-2026-71885. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-71885 affect?
CVE-2026-71885 affects Bouncy Castle (bc-java) < 1.86, Java applications using BouncyCastle MLS implementation, Deployments using MLS with X.509 credentials. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-71885?
Upgrade bc-java to >=1.86; validate MLS credential admission and audit group keys
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Attacker can present another's X.509 credential to join as that identity, evict victim, derive epoch, decrypt and send group messages as victim.
Immediate action required