CVE-2026-71888Network attack vectorHinoki check available

Authenticated-attribute integrity bypass via mismatched CMS fields

Published Oct 3, 2026 · Updated Oct 3, 2026

Authenticated-attribute integrity bypass in Bouncy Castle Java before 1.86 lets attackers insert unverified CMS attributes into valid messages. CMSAuthenticatedDataParser chooses what the MAC covers from digestAlgorithm before reading authAttrs, then exposes inserted attributes even though the MAC covered only the content. Exploitation requires control of a message in transit and an application that trusts those attributes for a decision; the content remains MAC-bound.

CVSS severityUnavailable
Unscored
EPSS probability0.11%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Authenticated-attribute integrity bypass in Bouncy Castle Java before 1.86 lets attackers insert unverified CMS attributes into valid messages. CMSAuthenticatedDataParser chooses what the MAC covers from digestAlgorithm before reading authAttrs, then exposes inserted attributes even though the MAC covered only the content. Exploitation requires control of a message in transit and an application that trusts those attributes for a decision; the content remains MAC-bound.

The record

CVE
CVE-2026-71888
Published
Oct 3, 2026
Updated
Oct 3, 2026
Vendor
Legion of the Bouncy Castle Inc.
Product
Bouncy Castle Java
Classifications
T1565.002
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?

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

  1. Affected versionversion=0 <1.86
  2. Affected versionversion=1.70 <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; version=1.70 <1.86
Legion of the Bouncy Castle Inc. · Bouncy Castle FIPS Java APIversion=1.0.0 <1.0.13; version=2.0.0 <2.0.13; version=2.0.0 <2.0.8; version=2.1.0 <2.1.13; version=2.1.0 <2.1.8
Legion of the Bouncy Castle Inc. · Bouncy Castle Java LTSversion=2.73.0 <2.73.13

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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1565.002Transmitted Data Manipulation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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