Signature Verification Flaw in Bouncy Castle for Java Affects Multiple Versions
CVE-2026-59639

8.7HIGH

Key Information:

Vendor

Legion Of The Bouncy Castle Inc.

Status
Bc-java
Bc-lts-java
Bc-fja
Vendor
CVE Published:
3 August 2026

What is CVE-2026-59639?

In Bouncy Castle for Java versions prior to 1.85, the CMS verifySignatures function incorrectly validates signatures for SignedData without any signers present. This flaw compromises the integrity of signed data, as a zero-signer condition would erroneously return true, potentially allowing malicious actors to exploit this vulnerability. The issue is present in both the regular and Long-Term Support (LTS) editions of Bouncy Castle, along with the FIPS-compliant versions. Updating to secure versions is essential to maintain your application's security and integrity.

Affected Version(s)

BC-FJA all 1.0.0 < 1.0.12

BC-FJA all 2.0.0 < 2.0.12

BC-FJA all 2.1.0 < 2.1.12

References

https://github.com/bcgit/bc-java/wiki/CVE-2026-59639
vendor-advisory
https://github.com/bcgit/bc-java/commit/99ddc6dcc6782e6a7...
patch

CVSS V4

Score:
8.7
Severity:
HIGH
Confidentiality:
None
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Alex Gaynor in collaboration with Claude and Anthropic Research
.