CVE-2026-63568
Unbounded CMP/CRMF password-based MAC iteration count allows CPU exhaustion
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Description
Allocation of resources without limits or throttling in the CMP/CRMF password-based MAC verifier (PKMacBuilder) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote unauthenticated attacker to cause a denial of service through CPU exhaustion via a CMP message or CRMF certificate request whose PBMParameter declares a very large iteration count, because PKMacBuilder enforced its iteration-count ceiling only when the caller had supplied an explicit maximum through the PKMacBuilder(IPKMacPrimitivesProvider, int) constructor. With any other constructor, ProtectedPkiMessage.Verify and CertificateRequestMessage.IsValidSigningKeyPop performed as many hash iterations as the sender requested, up to about 2^31, before the MAC could be checked.
Affected
Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.
Remediation
No guide yetNo remediation guidance has been written for this CVE yet. What the record does show:
Patch and advisory references
- https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63568
- https://github.com/bcgit/bc-csharp/commit/10a9862fad04bb0c832a78b10e71d9818d6d1a63
- https://github.com/bcgit/bc-csharp/commit/65283bae66843d0d3c13c5e0272dbbe1c0d6aa04
- https://github.com/bcgit/bc-csharp/commit/d16f08a53dd0a78eb3310bbe80c947c7e1677290
References (4)
SSVC — Action Prioritization
SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.
CVSS
- Attack Vector
- NETWORK
- Complexity
- LOW
- Privileges
- NONE
- User Interaction
- NONE
- Scope
- UNCHANGED
- Confidentiality
- NONE
- Integrity
- NONE
- Availability
- HIGH
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