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Bouncy Castle bc-java CVE-2026-59644

| EUVDEUVD-2026-52030 HIGH
Excessive Iteration (CWE-834)
2026-08-03 bcorg GHSA-xrmp-pcg8-5q9v
Java Information Disclosure Bc Java
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:N/VA:H/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
6.5 MEDIUM

Sender participates in authenticated MLS protocol (PR:L); pure CPU exhaustion with no confidentiality or integrity consequence (C:N/I:N/A:H).

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

Primary rating from Vendor (bcorg).

CVSS VectorVendor: bcorg

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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 - 01:34 vuln.today
Analysis Generated
Aug 03, 2026 - 01:34 vuln.today
CVE Published
Aug 03, 2026 - 00:50 cve.org
HIGH 8.7

DescriptionCVE.org

In Bouncy Castle for Java before 1.85, MLS hash-ratchet honours arbitrary 32-bit generation counter from sender.

AnalysisAI

CPU exhaustion in Bouncy Castle for Java's MLS (Messaging Layer Security) implementation allows a network attacker to trigger unbounded HKDF key-derivation iterations by supplying a crafted 32-bit generation counter in an MLS message. The hash-ratchet in GroupKeySet.get(int generation) advances one HKDF step per skipped generation without any upper bound, so a maximally crafted counter forces up to ~4.29 billion derivation steps on the receiving process. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Gain MLS group membership or inject wire message
Delivery
Craft MLS payload with generation counter near 2^32
Exploit
Deliver message to bc-java MLS endpoint
Execution
GroupKeySet.get() iterates ~4B HKDF steps
Persist
CPU exhaustion
Impact
Service unavailability
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Vulnerability AssessmentAI

Exploitation The target application must import and actively use bc-java's mls module artifact (not merely bc-java's core TLS or crypto APIs) and must process MLS group messages from senders outside full trust. … 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:N/VA:H scores 8.7 and signals a straightforward, remotely triggerable DoS with no complexity or privilege barriers per vendor assessment. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker who is an authenticated MLS group member - or who can inject a crafted MLS wire message prior to authentication verification - sends a message with the generation counter set to 0xFFFFFFFF (maximum 32-bit value). The receiving bc-java instance's GroupKeySet.get() enters a loop performing HKDF derivations for each of approximately 4.29 billion skipped generations, consuming all available CPU until the process is killed or becomes unresponsive. …
Remediation Upgrade Bouncy Castle for Java to version 1.85 or later, which caps forward ratchet steps at 65,536 (1 << 16) and rejects any generation counter more than that many steps ahead of the current generation. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours, identify all applications using Bouncy Castle for Java and determine their exposure to untrusted message traffic. …

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Module for Development Tools 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected
SUSE Linux Enterprise Server 16.0 Affected

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CVE-2026-59644 vulnerability details – vuln.today
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