Bug 2545494 (CVE-2026-71888)

Summary:	CVE-2026-71888 bouncycastle: bouncycastle-fips: Bouncy Castle: Security bypass via unvalidated attributes in CMS AuthenticatedData parser
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	amctagga, anthomas, ant, anujha, aoconnor, aschwart, asoldano, aszczucz, ataylor, bbaranow, bmaxwell, bniver, boliveir, bstansbe, cescoffi, csuconic, dbruscin, dfreiber, dlofthou, drichtar, drow, dschmidt, ehelms, flucifre, fmariani, fmongiar, gbenhaim, ggainey, gmalinko, gmeno, groman, gsmet, gtanzill, gtully, ikhan, istudens, ivassile, iweiss, janstey, jburrell, jbuscemi, jlanda, jmartisk, jnethert, jpasqual, jsherman, juwatts, jwon, kshier, kvanderr, manderse, mbenjamin, mcarlett, mdellweg, mhackett, mhulan, mosmerov, mposolda, msvehla, niyer, nmoumoul, nwallace, olubyans, osousa, ozzy, pberan, pcreech, pdelbell, pesilva, pjindal, pmackay, rbobbitt, rchan, rgemmell, rgodfrey, rguimara, rhel-process-autobot, rmartinc, rstancel, rstepani, sbiarozk, sdawley, simaishi, smallamp, sostapov, ssilvert, stcannon, sthorger, tbish, tcunning, thjenkin, tlavocat, tmalecek, twaugh, varjain, vdosoudi, vereddy, vkumar, vmuzikar, watson-tool-maintainers, yfang, yguenane
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in Bouncy Castle. In its Cryptographic Message Syntax (CMS) streaming parser, messages with mismatched attribute and algorithm fields are improperly handled, allowing attributes to be returned as valid even though they were not protected by the Message Authentication Code (MAC). A remote attacker capable of intercepting and modifying network traffic can exploit this flaw by inserting unauthorized attributes into an otherwise valid message. This can allow an attacker to manipulate application behavior and bypass security checks if the application relies on those attributes to make authorization or routing decisions.	Story Points:	---
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Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2550615, 2550616, 2550617
Bug Blocks:

Description OSIDB Bzimport 2026-10-03 08:51:19 UTC

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).