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Java CVE-2026-5598

| EUVDEUVD-2026-22872 HIGH
Covert Timing Channel (CWE-385)
2026-04-15 bcorg GHSA-p93r-85wp-75v3
Java Information Disclosure Bc Java Legion Of The Bouncy Castle Inc
8.9
CVSS 4.0 · Vendor: bcorg
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Identify FrodoKEM endpoint
  2. Delivery
    Send thousands of crafted key encapsulation requests
  3. Exploit
    Measure operation timing with microsecond precision
  4. Execution
    Apply statistical timing analysis to correlate delays with key bits
  5. Persist
    Reconstruct private key
  6. Impact
    Decrypt captured traffic or forge authenticated sessions

Vulnerability Assessment

Weakness
CWE
CWE-385
ASVS 5.0
V15 - Secure Coding and Architecture Covert timing channel
Exploitation Conditions

Exploitation requires the target system to be using BC-JAVA's FrodoKEM implementation for key encapsulation operations (e.g., post-quantum TLS cipher suites, hybrid key exchange protocols, or application-layer encrypted communications using FrodoKEM). Systems using BC-JAVA but not utilizing FrodoKEM features are not vulnerable despite running affected versions. Successful timing analysis demands network conditions allowing precise measurement of sub-millisecond timing variations, typically requiring attacker proximity (same datacenter, local network) or stable, low-jitter internet paths. Attackers need capability to initiate thousands to millions of cryptographic operations without rate limiting or detection. The CVSS vector (AV:N/AC:L/PR:N/UI:N) indicates no authentication barriers or user interaction required, but the AC:L (low complexity) rating understates the sophisticated statistical analysis and measurement infrastructure required for practical exploitation.
Impact

The CVSS 4.0 vector (AV:N/AC:L/PR:N/UI:N) indicates network-accessible exploitation requiring low complexity and no authentication, with catastrophic impact ratings (VC:H/VI:H/VA:H/SC:H/SI:H/SA:H) across all CIA triad dimensions in both vulnerable and subsequent systems. However, real-world risk is substantially lower than the 10.0 score suggests. EPSS probability of 0.04% (14th percentile) indicates security researchers assess actual exploitation likelihood as very low, despite theoretical severity. No active exploitation confirmed - absent from CISA KEV and no public proof-of-concept identified at time of analysis. SSVC rates exploitation status as 'none' but acknowledges the attack is automatable with total technical impact. The disconnect between maximum CVSS and minimal EPSS reflects that timing side-channel attacks against post-quantum KEMs require: (1) precise timing measurement capabilities, (2) thousands to millions of timing samples, (3) statistical expertise to extract key bits from noise, and (4) network conditions allowing sub-millisecond timing precision. These prerequisites make mass exploitation unlikely, though nation-state adversaries targeting high-value cryptographic systems could feasibly execute such attacks. Organizations using BC-JAVA for FrodoKEM operations in TLS handshakes or key establishment face genuine risk; those using other algorithms or not implementing FrodoKEM have zero exposure despite the broad CPE scope.
Exploit ScenarioDerived

An attacker initiates thousands of TLS handshakes or key encapsulation requests to a server using BC-JAVA's FrodoKEM implementation, precisely measuring response times for each cryptographic operation. By analyzing microsecond-level timing variations correlated with different inputs, the attacker applies statistical methods to distinguish computation paths dependent on private key bits. After collecting sufficient timing samples (typically 10,000-1,000,000 operations), the attacker reconstructs portions or entirety of the FrodoKEM private key, enabling decryption of past sessions (if traffic was recorded) and impersonation in future sessions.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv2 – Apr 16, 2026

Non-constant time comparison operations in the Legion of the Bouncy Castle BC-JAVA cryptographic library (core modules, versions 2.17.3 through 1.83) expose FrodoKEM private keys to timing side-channel attacks, enabling remote unauthenticated attackers to extract cryptographic secrets through statistical analysis of operation timing variations. CVSS 4.0 score of 10.0 reflects maximum confidentiality and integrity impact across system and subsequent contexts. EPSS probability is low (0.04%, 14th percentile) and no active exploitation is confirmed, but SSVC framework rates this as automatable with total technical impact. Vendor patch available in BC-JAVA 1.84.

Earlier versions of this analysis (1)
v1 Apr 15, 2026 - 12:38 CVSS 10.0

Non-constant time comparisons in Bouncy Castle BC-JAVA cryptographic library (versions 2.17.3 through 1.84 - note: likely versioning error in reporting) enable side-channel attacks against FrodoKEM post-quantum cryptographic operations, allowing remote unauthenticated attackers to extract private keys through timing analysis. This timing oracle vulnerability (CWE-385) achieves maximum CVSS 4.0 score of 10.0 due to network-exploitable covert channel with no attack complexity, no privileges required, and high impact across confidentiality, integrity, and availability in both vulnerable and subsequent system components. No confirmed active exploitation (not in CISA KEV), but the cryptographic nature and maximum severity score indicate critical risk for any deployment using FrodoKEM implementations in BC-JAVA.

RemediationAI

Upgrade BC-JAVA to version 1.84 or later, which contains vendor-released patches addressing the non-constant time comparison operations in FrodoKEM. Refer to the vendor security advisory at https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%905598 for specific upgrade guidance and release notes. For environments where immediate patching is not feasible, implement network-level timing jitter by deploying reverse proxies or load balancers that normalize response times, though this mitigation is incomplete as local network timing may still leak information. Consider temporarily disabling FrodoKEM cipher suites in TLS configurations if the post-quantum algorithm is not operationally required, reverting to classical ECDHE key exchange; this workaround eliminates post-quantum forward secrecy protections. Monitor cryptographic operations for unusual patterns of repeated connection attempts from single sources, which may indicate timing analysis attacks in progress. Prioritize patching for systems handling high-value cryptographic operations or exposed to nation-state threat actors.

Affected VersionsENISA

BC-JAVA 2.17.3 <1.84

Affected Packages

maven org.bouncycastle:bcprov-jdk14 fix: 1.81.1
maven org.bouncycastle:bcprov-jdk15to18 fix: 1.80.2
maven org.bouncycastle:bcprov-jdk18on fix: 1.84
euvd bc_java fix: 1.84

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 4 packages in maven, euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

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Technical ContextAI · show details

This vulnerability affects the FrodoKEM post-quantum cryptographic implementation in Bouncy Castle's BC-JAVA library. FrodoKEM is a lattice-based Key Encapsulation Mechanism (KEM) selected for NIST post-quantum cryptography standardization. The flaw (CWE-385: Covert Timing Channel) stems from non-constant time comparison operations during cryptographic computations. Constant-time implementations are critical in cryptography because branching or conditional operations based on secret values cause measurable timing variations. Attackers can perform statistical timing analysis across thousands of operations to deduce bits of the private key. Bouncy Castle BC-JAVA is a widely-deployed Java cryptography provider used for SSL/TLS, code signing, and encrypted communications. The affected CPE (cpe:2.3:a:legion_of_the_bouncy_castle_inc.:bc-java) encompasses all core modules from version 2.17.3 up to but not including 1.84, though the version range notation appears inconsistent and should be verified against the vendor advisory.

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Severity by source

Vendor (bcorg) PRIMARY 8.9 HIGH
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N/E:U/S:P/AU:Y/U:Red
SUSE 8.6 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L
Red Hat 7.5 HIGH

Primary rating from Vendor (bcorg).

CVSS VectorVendor: bcorg

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Vulnerable system: Confidentiality
High
Vulnerable system: Integrity
High
Vulnerable system: Availability
None
Subsequent system: Confidentiality
High
Subsequent system: Integrity
High
Subsequent system: Availability
None

Lifecycle Timeline

5
Patch released
Apr 21, 2026 - 16:16 nvd
Patch available
Severity Changed
Apr 21, 2026 - 15:22 NVD
CRITICAL HIGH
CVSS changed
Apr 21, 2026 - 15:22 NVD
10.0 (CRITICAL) 8.9 (HIGH)
Patch available
Apr 16, 2026 - 05:29 EUVD
1.84
CVE Published
Apr 15, 2026 - 09:05 nvd
HIGH 8.9

DescriptionCVE.org

Covert timing channel vulnerability in Legion of the Bouncy Castle Inc. BC-JAVA core on all (core modules). Non-constant time comparisons risk private key leakage in FrodoKEM.

This issue affects BC-JAVA: from 2.17.3 before 1.84.

Blast Radius

ecosystem impact
† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth
  • 5 maven packages depend on org.bouncycastle:bcprov-jdk14 (2 direct, 3 indirect)
  • 295 maven packages depend on org.bouncycastle:bcprov-jdk15to18 (58 direct, 240 indirect)
  • 4,246 maven packages depend on org.bouncycastle:bcprov-jdk18on (627 direct, 3,627 indirect)

Ecosystem-wide dependent count for version 1.81 and other introduced versions.

Executive ViewAI

Why It Matters

CVE-2026-5598 is a critical timing side-channel vulnerability in Bouncy Castle BC-JAVA cryptographic library (versions 1.74-1.83) that allows remote attackers to extract FrodoKEM private keys through statistical analysis of operation timing. Organizations using BC-JAVA for cryptographic operations face confidentiality compromise of sensitive keys without requiring authentication, potentially undermining the security of encrypted communications and digital signatures across dependent applications.

Business Impact: Severe
Compensating Controls

Apply vendor patch. Bounty Castle has released BC-JAVA version 1.84 addressing the timing side-channel vulnerability. Until patching is complete, restrict network access to services using vulnerable library versions and disable FrodoKEM operations if alternative algorithms are available.

Threat Intelligence Overview

EPSS Score
0.0%
Top 86% exploitable
Threat Intel
1
1 source
Social Media
1
Sightings
Data Quality
8 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment GHSA Vendor CIRCL GitHub VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity HIGH
CISA KEV No
Public POC No
EPSS 0.0%
Patch available Yes
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision
Out-of-Cycle
Exploitation
None
System Exposure· derived
Open
Automatable
Yes
Human Impact
Very High
Technical Impact
Total

Priority Score

44
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +44
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

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Vendor StatusVendor

SUSE

Severity: High
Product Status
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
SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS Affected
SUSE Linux Enterprise Module for Development Tools 15 SP7 Affected

References

Advisories & patches
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-5598 ADVISORY https://vuldb.com/vuln/357694 REF https://access.redhat.com/errata/RHSA-2026:12267 REF https://access.redhat.com/errata/RHSA-2026:12269 REF https://access.redhat.com/errata/RHSA-2026:18054 REF https://access.redhat.com/errata/RHSA-2026:18055 REF https://access.redhat.com/errata/RHSA-2026:18059 REF https://access.redhat.com/errata/RHSA-2026:53644 REF https://access.redhat.com/errata/RHSA-2026:53645 REF https://access.redhat.com/errata/RHSA-2026:53646 REF https://access.redhat.com/errata/RHSA-2026:53806 REF https://access.redhat.com/security/cve/CVE-2026-5598 REF https://bugzilla.redhat.com/show_bug.cgi?id=2458635 REF https://github.com/bcgit/bc-java/commit/8692e6b2b191fc4aafa32545c7a78bdb9bf110c5 REF https://github.com/bcgit/bc-java/commit/94abbd56413dfdac651fd878bc60253871ef5e87 REF https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%905598 REF https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%905998 REF https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5598.json

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