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Bouncy Castle Java CVE-2026-12860

| EUVDEUVD-2026-52138 HIGH
Improper Verification of Cryptographic Signature (CWE-347)
2026-08-03 bcorg GHSA-cggx-vw4r-j93f
Java Information Disclosure Jwt Attack Bc Java Bc Lts Java 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
5.9 MEDIUM

Network-reachable forgery, no auth required, but AC:H because the NULL-omitted DigestInfo code path must be active in the target application.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
4.0 AV:N/AC:L/AT:P/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 - 04:22 vuln.today
Analysis Generated
Aug 03, 2026 - 04:22 vuln.today
CVE Published
Aug 03, 2026 - 02:55 cve.org
HIGH 8.7

DescriptionCVE.org

In Bouncy Castle for Java before 1.85, RSA PKCS#1 verification skips last two hash bytes in NULL-omitted path. This issue also affects Bouncy Castle for Java LTS before 2.73.12.

AnalysisAI

RSA PKCS#1 v1.5 signature forgery is possible in Bouncy Castle for Java (bc-java before 1.85, bc-lts-java before 2.73.12) when the DigestInfo encoding omits the NULL AlgorithmIdentifier parameter. The off-by-two bytes in the RSADigestSigner comparison loop allows any forged signature whose DigestInfo matches all bytes except the final two of the message hash to pass verification as valid, achieving a high-integrity bypass. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Craft NULL-omitted DigestInfo with last two hash bytes altered
Delivery
Generate RSA signature over forged DigestInfo structure
Exploit
Submit forged signature to Bouncy Castle verification endpoint
Execution
Off-by-two loop skips final two hash bytes
Persist
Forged signature accepted as valid
Impact
Integrity bypass achieved
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Vulnerability AssessmentAI

Exploitation Exploitation requires that the target application uses Bouncy Castle's RSADigestSigner for RSA PKCS#1 v1.5 signature verification AND that the signer or signing library producing the signatures being verified uses the legacy NULL-omitted AlgorithmIdentifier encoding in DigestInfo (rather than the RFC 8017-compliant NULL-present encoding). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 score of 8.7 with vector AV:N/AC:L/AT:N/PR:N/UI:N/VI:H reflects unauthenticated remote exploitation with high integrity impact and no confidentiality or availability impact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker targets a Java application using Bouncy Castle to verify RSA-signed JWTs. The attacker computes the SHA-256 hash of their target message, flips the final two hash bytes, encodes this in a NULL-omitted DigestInfo structure, and generates an RSA signature over the forged structure. …
Remediation Upgrade Bouncy Castle for Java (bc-java) to version 1.85 or later, or Bouncy Castle for Java LTS (bc-lts-java) to version 2.73.12 or later, as documented in the vendor advisory at https://github.com/bcgit/bc-java/wiki/CVE-2026-12860 and fixed in commit https://github.com/bcgit/bc-java/commit/ea5970ea9b2fb91d763b904692fd21089ca3e396. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Identify all applications using Bouncy Castle for Java within 24 hours. …

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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-2026-12860 vulnerability details – vuln.today
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