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Bouncy Castle Java CVE-2026-12802

| EUVDEUVD-2026-52133 HIGH
Improper Validation of Integrity Check Value (CWE-354)
2026-08-03 bcorg GHSA-833g-4xxm-r9cx
Java Information Disclosure Bc Java Bc Lts Java Bc Fja Suse
8.7
CVSS 4.0 · Vendor: bcorg
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Severity by source

Vendor (bcorg) PRIMARY
8.7 HIGH
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
vuln.today AI
7.5 HIGH

Network-delivered CMS payload requires no authentication or user interaction; no confidentiality or availability impact, only integrity via AEAD tag downgrade.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
SUSE
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Primary rating from Vendor (bcorg).

CVSS VectorVendor: bcorg

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
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

3
Source Code Evidence Fetched
Aug 03, 2026 - 04:26 vuln.today
Analysis Generated
Aug 03, 2026 - 04:26 vuln.today
CVE Published
Aug 03, 2026 - 02:48 cve.org
HIGH 8.7

DescriptionCVE.org

In Bouncy Castle for Java before 1.85, CMS AuthEnvelopedData fails to enforce tag-length on decryption. This issue also affects Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) before bcpkix-fips 1.0.12 (1.0.X series), 2.0.12 (2.0.X series) and 2.1.12 (2.1.X series).

AnalysisAI

CMS AuthEnvelopedData decryption in Bouncy Castle for Java fails to enforce a minimum AEAD authentication tag length, allowing a network attacker to supply a crafted CMS message carrying a truncated AES-GCM/CCM ICV (e.g., 32 bits instead of the standard 128 bits), effectively reducing the authentication space to the point where tag forgery becomes computationally feasible. Affected are bc-java before 1.85, bc-lts-java before 2.73.12, and all bc-fja (FIPS) 1.0.x/2.0.x/2.1.x series before their respective .12 patch releases. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Obtain target recipient's public key or certificate
Delivery
Craft CMS AuthEnvelopedData with downgraded 32-bit AES-GCM tag
Exploit
Deliver crafted message to vulnerable application endpoint
Execution
Bouncy Castle decrypts without enforcing minimum tag length
Persist
Brute-force AEAD tag collision with ~2^32 attempts
Impact
Forge authenticated ciphertext accepted as genuine
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Vulnerability AssessmentAI

Exploitation The application must use Bouncy Castle's CMS AuthEnvelopedData decryption path - specifically, one of the JCE recipient types (JceKeyTransRecipient, JceKeyAgreeRecipient, JceKEMRecipient, JcePasswordRecipient, or JceKEKRecipient) - and must process CMS messages received from an attacker-controlled or attacker-influenceable source. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N) signals high integrity impact with no authentication, no complexity barrier, and no user interaction required - a strong paper score. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker targeting a Java-based secure document exchange platform that accepts inbound CMS AuthEnvelopedData payloads crafts a malicious message encrypted for the target recipient's public key but specifying a 32-bit AES-GCM ICV in the AlgorithmIdentifier. The vulnerable Bouncy Castle recipient decrypts the message without validating the tag length, accepting the weakened authentication guarantee. …
Remediation Upgrade to Bouncy Castle for Java 1.85 or later, bc-lts-java 2.73.12 or later, or the appropriate FIPS patch release (bcpkix-fips 1.0.12, 2.0.12, or 2.1.12 depending on the series in use), as detailed in the vendor advisory at https://github.com/bcgit/bc-java/wiki/CVE-2026-12802. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: Conduct dependency scanning across all production and development environments to identify applications using bc-java, bc-lts-java, or bc-fja and build an inventory by version. …

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
openSUSE Leap 16.0 Fixed
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Affected

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CVE-2026-12802 vulnerability details – vuln.today
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