{
  "cveId": "CVE-2026-71885",
  "url": "https://patchblox.com/security/cve/CVE-2026-71885",
  "summary": "CVE-2026-71885 is fixed in bouncycastle on 1 platform, first by DEBIAN-CVE-2026-71885, released October 3, 2026. It is not reported as exploited. Patch Radar priority: Routine.",
  "title": "bouncycastle: In Bouncy Castle for Java before 1.86, the Messaging Layer Security (MLS, RFC 9420) implementation did not bind an X....",
  "description": "In Bouncy Castle for Java before 1.86, the Messaging Layer Security (MLS, RFC 9420) implementation did not bind an X.509 credential to a LeafNode\u0027s signature_key. LeafNode.verify() checked a leaf\u0027s signature against the signature_key carried in the leaf itself, while the credential\u0027s X.509 certificate chain was stored but never parsed or validated, so the end-entity certificate\u0027s public key was never required to match signature_key as RFC 9420 sec. 5.3 requires. A party could therefore present another party\u0027s certificate as its credential while signing the leaf, and the enclosing KeyPackage, with an unrelated key, and be accepted under that other party\u0027s identity through KeyPackage.verify() and the Group leaf-validation path. In a deployment that admits external commits without an independent credential-admission check, an unauthenticated attacker could be admitted under a victim\u0027s X.509 identity, evict the victim (resynchronization compares whole credentials rather than signing keys), derive the current epoch, decrypt subsequent group messages, and send messages accepted as the victim. TreeKEM.LeafNode now requires the end-entity certificate\u0027s subject public key, in the cipher suite\u0027s signature encoding, to equal signature_key for an X.509 credential and rejects the leaf otherwise, including an empty chain or a certificate whose key type does not match the cipher suite; certificate-chain and identity validation to a trust anchor remain the application\u0027s responsibility per RFC 9420 sec. 5.3.1. Deployments using only basic credentials are unaffected.",
  "published": "2026-10-03T09:17:04Z",
  "severity": "",
  "epss": 0.00198,
  "epssPercentile": 0.09673,
  "priority": "Routine",
  "priorityTier": 4,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "fixes": [
    {
      "platform": "linux",
      "product": "bouncycastle",
      "release": "Debian 14",
      "fixedVersion": "1.86-1",
      "fix": "DEBIAN-CVE-2026-71885",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2026-71885",
      "released": "2026-10-03T21:16:35Z"
    },
    {
      "platform": "linux",
      "product": "bouncycastle",
      "release": "opensuse-leap 16.0",
      "fixedVersion": "1.86-160000.1.1",
      "fix": "OPENSUSE-SU-2026:22169-1",
      "url": "https://patchblox.com/security/fix/linux/opensuse-su-2026-22169-1",
      "released": "2026-11-07T00:47:19Z"
    },
    {
      "platform": "linux",
      "product": "bouncycastle",
      "release": "sles 15.6",
      "fixedVersion": "1.86-150200.3.41.1",
      "fix": "SUSE-SU-2026:4797-1",
      "url": "https://patchblox.com/security/fix/linux/suse-su-2026-4797-1",
      "released": "2026-11-07T00:42:08Z"
    },
    {
      "platform": "linux",
      "product": "bouncycastle",
      "release": "sles 15.7",
      "fixedVersion": "1.86-150200.3.41.1",
      "fix": "SUSE-SU-2026:4797-1",
      "url": "https://patchblox.com/security/fix/linux/suse-su-2026-4797-1",
      "released": "2026-11-07T00:42:08Z"
    },
    {
      "platform": "linux",
      "product": "bouncycastle",
      "release": "sles 16.0",
      "fixedVersion": "1.86-160000.1.1",
      "fix": "SUSE-SU-2026:24461-1",
      "url": "https://patchblox.com/security/fix/linux/suse-su-2026-24461-1",
      "released": "2026-11-07T00:44:01Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-08T00:53:09Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}