CVE-2026-58063 Legion of the Bouncy Castle Inc. CVE debrief

Who should care

Organizations using Bouncy Castle for Java library versions before 1.85, as well as those using Bouncy Castle for Java LTS before 2.73.12 and Bouncy Castle for Java FIPS (BC-FJA) before specific versions, should be aware of this vulnerability and take necessary actions to upgrade or mitigate the risk. This includes security teams, vulnerability management teams, and operators of systems that utilize Bouncy Castle for Java. Additionally, platform administrators and security personnel responsible for monitoring and incident response should be informed about the potential impacts of this vulnerability.

Technical summary

The Bouncy Castle for Java library before version 1.85 has a vulnerability in the BCFKS keystore load functionality, which honours unbounded KDF cost from untrusted files. This issue also affects Bouncy Castle for Java LTS before 2.73.12 and Bouncy Castle for Java FIPS (BC-FJA) before specific versions. The vulnerability has a CVSS score of 5.3, indicating a medium severity level. The unbounded KDF cost issue could potentially lead to performance degradation or denial-of-service conditions. Organizations using affected versions of Bouncy Castle for Java should prioritize upgrading to a secure version.

Defensive priority

Medium priority given the CVSS score of 5.3 and the potential for unbounded KDF cost issues.

Recommended defensive actions

• Verify Bouncy Castle for Java version and upgrade to 1.85 or later if necessary.
• Review and adjust KDF cost settings for BCFKS keystore loads.
• Monitor for any suspicious activity related to keystore loads.
• Perform a thorough review of the Bouncy Castle for Java library usage within the organization.
• Check for any exposed systems that require compensating controls while remediation is scheduled.
• Track exceptions and retest remediated assets.
• Review relevant monitoring, detection, and logs for exposed assets that need extra review.

Evidence notes

The evidence for CVE-2026-58063 is limited; primary official records indicate Bouncy Castle for Java before 1.85 has an issue with BCFKS keystore load honouring unbounded KDF cost from untrusted files. Defenders should verify Bouncy Castle for Java versions in use, review KDF cost settings, and monitor for suspicious activity related to keystore loads. Additional verification tasks may be necessary based on specific deployment contexts.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.