CVE-2026-71887Hinoki check available

Signature misattribution via missing subkey cross-certification

Published Oct 3, 2026 · Updated Oct 3, 2026

OpenPGP signature misattribution in Bouncy Castle Java 1.81 through 1.85.2 allows attackers to claim genuine signatures under their own certificates. OpenPGPCertificate inherits signing flags from the primary key when a subkey binding omits Key Flags, while its cross-certification check reads only that binding and skips the required back signature. Exploitation requires a victim's public signing subkey and a message that subkey genuinely signed; it does not forge a new signature or expose the private key.

CVSS severityUnavailable
Unscored
EPSS probability0.09%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

OpenPGP signature misattribution in Bouncy Castle Java 1.81 through 1.85.2 allows attackers to claim genuine signatures under their own certificates. OpenPGPCertificate inherits signing flags from the primary key when a subkey binding omits Key Flags, while its cross-certification check reads only that binding and skips the required back signature. Exploitation requires a victim's public signing subkey and a message that subkey genuinely signed; it does not forge a new signature or expose the private key.

The record

CVE
CVE-2026-71887
Published
Oct 3, 2026
Updated
Oct 3, 2026
Vendor
Legion of the Bouncy Castle Inc.
Product
Bouncy Castle Java
Classifications
Unavailable
Attack vector
Unavailable
Privileges
Unavailable

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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.81 <1.86

What conditions does exploitation require?

Attack vectorUnavailable in this record.
Required privilegesUnavailable in this record.

What is affected?

Legion of the Bouncy Castle Inc. · Bouncy Castle Javaversion=1.81 <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.

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)
VectorUnavailable
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

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Technologies

Your stack

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Your stack

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