Denial of Service Vulnerability in Bouncy Castle bc-csharp Library
CVE-2026-63568

8.7HIGH

Key Information:

Vendor

Legion Of The Bouncy Castle Inc.

Status
Bc-csharp
Vendor
CVE Published:
2 October 2026

What is CVE-2026-63568?

A vulnerability exists in the bc-csharp library's PKMacBuilder component, which allows attackers to exploit the CMP/CRMF password-based MAC verifier. This can lead to denial of service through CPU exhaustion when a remote unauthenticated attacker sends specific CMP messages or CRMF certificate requests that declare an excessively large iteration count. The issue is mainly due to the failure to enforce an iteration-count ceiling unless the user explicitly specifies a maximum in the constructor. As a result, functions such as ProtectedPkiMessage.Verify and CertificateRequestMessage.IsValidSigningKeyPop may execute a staggering number of hash iterations, potentially reaching up to 2^31, before the message authentication code (MAC) verification takes place.

Affected Version(s)

bc-csharp 0 < 2.7.0

References

https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63568
vendor-advisory
https://github.com/bcgit/bc-csharp/commit/10a9862fad04bb0...
patch
https://github.com/bcgit/bc-csharp/commit/65283bae66843d0...
patch

CVSS V4

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

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Discovered by Claude, Anthropic's AI assistant, and triaged by the Anthropic security team in collaboration with Anthropic Research.
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