CMS AuthenticatedData exposes attacker-inserted authAttrs when digestAlgorithm is absent

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-71888
StatePUBLISHED
Assignerbcorg
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-03 09:17:05 UTC
Updated2026-10-03 09:17:05 UTC
DescriptionIn 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).

Risk And Classification

Primary CVSS: v4.0 8.7 HIGH from 91579145-5d7b-4cc5-b925-a0262ff19630

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber

Problem Types: CWE-354 | CWE-354 CWE-354 Improper Validation of Integrity Check Value

VersionSourceTypeScoreSeverityVector
4.091579145-5d7b-4cc5-b925-a0262ff19630Secondary8.7HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/C...
4.0CNACVSS8.7HIGHCVSS: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 v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality
None
Integrity
High
Availability
None
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Legion Of The Bouncy Castle Inc. BC-JAVA affected 1.86 maven all
CNA Legion Of The Bouncy Castle Inc. BC-JAVA affected 1.70 1.86 maven all
CNA Legion Of The Bouncy Castle Inc. BC-LTS-JAVA affected 2.73.0 2.73.13 maven all
CNA Legion Of The Bouncy Castle Inc. BC-LTS-JAVA affected 2.73.0 2.73.13 maven all
CNA Legion Of The Bouncy Castle Inc. BC-FJA affected 1.0.0 1.0.13 maven all
CNA Legion Of The Bouncy Castle Inc. BC-FJA affected 2.0.0 2.0.13 maven all
CNA Legion Of The Bouncy Castle Inc. BC-FJA affected 2.1.0 2.1.13 maven all
CNA Legion Of The Bouncy Castle Inc. BC-FJA affected 2.0.0 2.0.8 maven all
CNA Legion Of The Bouncy Castle Inc. BC-FJA affected 2.1.0 2.1.8 maven all

References

ReferenceSourceLinkTags
github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071888 91579145-5d7b-4cc5-b925-a0262ff19630 github.com
github.com/bcgit/bc-java/commit/dcb683b32b440f1beb1d2276a34930164281fb95 91579145-5d7b-4cc5-b925-a0262ff19630 github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Bhargava Shastry (en)

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