CVE-2026-71890Network attack vectorHinoki check available

Unauthenticated group-member eviction via unchecked external-commit removal

Published Oct 3, 2026 · Updated Oct 3, 2026

Incorrect authorization in Bouncy Castle Java 1.73 through 1.85 allows remote attackers to evict an MLS group member via an external commit. Group.validateExternalCachedProposals bounds the Remove leaf index but never checks that its credential belongs to the external joiner. An attacker needs the group's public GroupInfo and a target LeafIndex; accepting members then remove that participant and give the joiner the vacated tree slot.

CVSS severity8.7
High
EPSS probability0.25%
Next 30 days · Oct 18, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
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Summary

What happened

Incorrect authorization in Bouncy Castle Java 1.73 through 1.85 allows remote attackers to evict an MLS group member via an external commit. Group.validateExternalCachedProposals bounds the Remove leaf index but never checks that its credential belongs to the external joiner. An attacker needs the group's public GroupInfo and a target LeafIndex; accepting members then remove that participant and give the joiner the vacated tree slot.

The record

CVE
CVE-2026-71890
Published
Oct 3, 2026
Updated
Oct 3, 2026
Vendor
Legion of the Bouncy Castle Inc.
Product
Bouncy Castle Java
Classifications
CWE-863, T1531
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=1.73 <1.86

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Legion of the Bouncy Castle Inc. · Bouncy Castle Javaversion=1.73 <1.86

Published CVSS scores

8.7Legion of the Bouncy Castle Inc.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

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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

CWE-863Incorrect Authorization
T1531Account Access Removal

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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