CVE-2026-71888CMS AuthenticatedData exposes attacker-inserted authAttrs when digestAlgorithm is absent
Updated under an hour ago ()
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It affects Legion of the Bouncy Castle Inc. BC-JAVA and 2 other products. Add what you run to find out whether that includes you.
EPSS puts the chance of exploitation in the next 30 days at 0.11%, higher than 1% of scored CVEs.
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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).
- CVSS
- 8.7 HIGH (v4.0, CNA)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
- Weakness (CWE)
- CWE-354
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- 0.11% (percentile 1)
- Assigned by
- bcorg
- NVD analysis
- Awaiting Analysis
- Record last updated
- Oct 5, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Legion of the Bouncy Castle Inc. BC-JAVA legion_of_the_bouncy_castle:bc_java (from the name) | before 1.86 | CNA record |
Legion of the Bouncy Castle Inc. BC-LTS-JAVA legion_of_the_bouncy_castle:bc_lts_java (from the name) | from 2.73.0 before 2.73.13 | CNA record |
Legion of the Bouncy Castle Inc. BC-FJA legion_of_the_bouncy_castle:bc_fja (from the name) | from 1.0.0 before 1.0.13; from 2.0.0 before 2.0.13; from 2.1.0 before 2.1.13 | CNA record |
References
- https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071888vendor-advisory
- https://github.com/bcgit/bc-java/commit/dcb683b32b440f1beb1d2276a34930164281fb95patch
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.