CVE-2026-71888 - Vulnerability Details - OpenCVE

In Bouncy Castle for Java before 1.86, the streaming CMS AuthenticatedData parser accepted a message whose digestAlgorithm and authAttrs fields disagreed about whether authenticated attributes were present. RFC 5652 sec. 9.1 pairs the two, requiring that authAttrs be present whenever digestAlgorithm is, and sec. 9.2 makes the MAC cover the DER encoding of authAttrs when they are present and the eContent OCTET STRING directly when they are not. CMSAuthenticatedDataParser has to choose between those two in its constructor, before it can reach authAttrs, which comes later in the SEQUENCE, so it chose on digestAlgorithm alone: for a message with digestAlgorithm absent but authAttrs present it verified the content MAC and then returned the attributes through getAuthAttrs() as though they had been authenticated, when the MAC had never covered them. An attacker able to modify a message in transit could insert an authenticated attribute, such as an RFC 2634 ESSSecurityLabel, into an otherwise valid message while holding neither the key-encryption key nor the content-MAC key, and an application taking an authorization, routing or labelling decision from those attributes would act on attacker-chosen values. The content itself remained MAC-bound. asn1.cms.AuthenticatedData now rejects the mismatched pairing when parsing and CMSAuthenticatedDataParser cross-checks the two fields once authAttrs is read. This is a variant of CVE-2026-59642, which bound the content to the MAC for messages that legitimately carry authAttrs, and which does not address this case. This issue also affects Bouncy Castle for Java LTS before 2.73.13, and Bouncy Castle for Java FIPS (BC-FJA) before bcpkix-fips 1.0.13 (1.0.X series), 2.0.13 (2.0.X series) and 2.1.13 (2.1.X series), and bcutil-fips 2.0.8 (2.0.X series) and 2.1.8 (2.1.X series).

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact High

Vulnerable System Availability Impact None

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

No CVSS v3.1

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Legion of the Bouncy Castle Inc.

BC-JAVA

unaffected

Version	Status	Constraints
`0`	affected	< 1.86

Legion of the Bouncy Castle Inc.

BC-JAVA

unaffected

Version	Status	Constraints
`1.70`	affected	< 1.86

Legion of the Bouncy Castle Inc.

BC-LTS-JAVA

unaffected

Version	Status	Constraints
`2.73.0`	affected	< 2.73.13

Legion of the Bouncy Castle Inc.

BC-LTS-JAVA

unaffected

Version	Status	Constraints
`2.73.0`	affected	< 2.73.13

Legion of the Bouncy Castle Inc.

BC-FJA

unaffected

Version	Status	Constraints
`1.0.0`	affected	< 1.0.13
`2.0.0`	affected	< 2.0.13
`2.1.0`	affected	< 2.1.13

Legion of the Bouncy Castle Inc.

BC-FJA

unaffected

Version	Status	Constraints
`2.0.0`	affected	< 2.0.8
`2.1.0`	affected	< 2.1.8

No data.

No data.

No data.

Project Subscriptions

No data.

Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References

Link	Providers
https://github.com/bcgit/bc-java/commit/dcb683b32b440f1beb1d2276a34930164281fb95
https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071888

History

Sat, 03 Oct 2026 08:45:00 +0000

Type	Values Removed	Values Added
Description		In Bouncy Castle for Java before 1.86, the streaming CMS AuthenticatedData parser accepted a message whose digestAlgorithm and authAttrs fields disagreed about whether authenticated attributes were present. RFC 5652 sec. 9.1 pairs the two, requiring that authAttrs be present whenever digestAlgorithm is, and sec. 9.2 makes the MAC cover the DER encoding of authAttrs when they are present and the eContent OCTET STRING directly when they are not. CMSAuthenticatedDataParser has to choose between those two in its constructor, before it can reach authAttrs, which comes later in the SEQUENCE, so it chose on digestAlgorithm alone: for a message with digestAlgorithm absent but authAttrs present it verified the content MAC and then returned the attributes through getAuthAttrs() as though they had been authenticated, when the MAC had never covered them. An attacker able to modify a message in transit could insert an authenticated attribute, such as an RFC 2634 ESSSecurityLabel, into an otherwise valid message while holding neither the key-encryption key nor the content-MAC key, and an application taking an authorization, routing or labelling decision from those attributes would act on attacker-chosen values. The content itself remained MAC-bound. asn1.cms.AuthenticatedData now rejects the mismatched pairing when parsing and CMSAuthenticatedDataParser cross-checks the two fields once authAttrs is read. This is a variant of CVE-2026-59642, which bound the content to the MAC for messages that legitimately carry authAttrs, and which does not address this case. This issue also affects Bouncy Castle for Java LTS before 2.73.13, and Bouncy Castle for Java FIPS (BC-FJA) before bcpkix-fips 1.0.13 (1.0.X series), 2.0.13 (2.0.X series) and 2.1.13 (2.1.X series), and bcutil-fips 2.0.8 (2.0.X series) and 2.1.8 (2.1.X series).
Title		CMS AuthenticatedData exposes attacker-inserted authAttrs when digestAlgorithm is absent
Weaknesses		CWE-354
References		https://github.com/bcgit/bc-java/commit/dcb683b32b440f1beb1d2276a34930164281fb95 https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071888
Metrics		cvssV4_0 `{'score': 8.7, 'vector': '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'}`

Projects

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MITRE

Status: PUBLISHED

Assigner: bcorg

Published: 2026-10-03T08:36:12.960Z

Updated: 2026-10-03T08:36:12.960Z

Reserved: 2026-08-08T00:06:07.401Z

Link: CVE-2026-71888

Vulnrichment

No data.

NVD

No data.

Redhat

No data.

OpenCVE Enrichment

No data.

Weaknesses

CWE-354

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CMSAuthenticatedDataParser has to choose between those two in its constructor, before it can reach authAttrs, which comes later in the SEQUENCE, so it chose on digestAlgorithm alone: for a message with digestAlgorithm absent but authAttrs present it verified the content MAC and then returned the attributes through getAuthAttrs() as though they had been authenticated, when the MAC had never covered them. An attacker able to modify a message in transit could insert an authenticated attribute, such as an RFC 2634 ESSSecurityLabel, into an otherwise valid message while holding neither the key-encryption key nor the content-MAC key, and an application taking an authorization, routing or labelling decision from those attributes would act on attacker-chosen values. The content itself remained MAC-bound. asn1.cms.AuthenticatedData now rejects the mismatched pairing when parsing and CMSAuthenticatedDataParser cross-checks the two fields once authAttrs is read. 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