X.509 Name Constraints Bypass Vulnerability in Bouncy Castle for Java
CVE-2026-71889

8.7HIGH

Key Information:

Vendor

Legion Of The Bouncy Castle Inc.

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

What is CVE-2026-71889?

The Bouncy Castle for Java library prior to version 1.86 exhibits a vulnerability where the PKIXCertPathReviewer fails to apply X.509 name constraints to end-entity certificates. The flaw arises because the method for verifying name constraints does not properly assess the target certificate during the validation process, potentially allowing certificates to be accepted even if they violate the issuing CA's constraints. This oversight can lead applications to make unauthorized trust decisions, undermining their security posture. Subsequent updates have addressed this issue by ensuring that all certificates in the validation path, including the target certificate, are appropriately validated against specified constraints.

Affected Version(s)

BC-FJA all 1.0.4 < 1.0.13

BC-FJA all 2.0.0 < 2.0.13

BC-FJA all 2.1.0 < 2.1.13

References

https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2...
vendor-advisory
https://github.com/bcgit/bc-java/commit/06dcff2f51037095d...
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

Yu Bao from the PayPal Cyber Security Team
.