CVE-2026-71885Network attack vectorHinoki check available

Group impersonation via unbound MLS certificate key

Published Oct 3, 2026 · Updated Oct 3, 2026

Identity spoofing in the MLS API of Bouncy Castle Java before 1.86 allows remote attackers to join groups under another member's X.509 identity. LeafNode.verify() checks a leaf signature against its declared signature_key but does not compare that key with the public key in the supplied certificate. Exploitation requires an application to accept external commits without an independent credential-admission check; an admitted attacker can read subsequent group messages and send messages as the victim.

CVSS severityUnavailable
Unscored
EPSS probability0.19%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Identity spoofing in the MLS API of Bouncy Castle Java before 1.86 allows remote attackers to join groups under another member's X.509 identity. LeafNode.verify() checks a leaf signature against its declared signature_key but does not compare that key with the public key in the supplied certificate. Exploitation requires an application to accept external commits without an independent credential-admission check; an admitted attacker can read subsequent group messages and send messages as the victim.

The record

CVE
CVE-2026-71885
Published
Oct 3, 2026
Updated
Oct 3, 2026
Vendor
Legion of the Bouncy Castle Inc.
Product
Bouncy Castle Java
Classifications
T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Oct 3, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=0 <1.86

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Legion of the Bouncy Castle Inc. · Bouncy Castle Javaversion=0 <1.86

Published CVSS scores

No CVSS assessment is available in this record.

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

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No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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