CVE-2026-63568
Received Received - Intake

Allocation of Resources Without Limits in Bouncy Castle CMP/CRMF MAC Verifier

Publication date: 2026-10-02

Last updated on: 2026-10-02

Assigner: bcorg

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.

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Meta Information

Published
2026-10-02
Last Modified
2026-10-02
Generated
2026-10-02
AI Q&A
2026-10-02
EPSS Evaluated
N/A
NVD
CVE-2026-63568
EUVD
EUVD-2026-91219

Affected Vendors & Products

Showing 3 associated CPEs
Vendor Product Version / Range
bouncy_castle bc-csharp to 2.7.0 (exc)
bouncy_castle bc_csharp to 2.7.0 (exc)
bouncy_castle bc_csharp From 2.6.2 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-770 The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.

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Executive Summary

CVE-2026-63568 is a denial-of-service vulnerability in the Bouncy Castle C# library's PKMacBuilder class. It allows a remote attacker to cause CPU exhaustion by sending a CMP message or CRMF certificate request with a very large iteration count in the PBMParameter. The issue occurs because PKMacBuilder did not enforce iteration limits unless explicitly configured, allowing up to 2^31 hash iterations before MAC verification.

Detection Guidance

To detect this vulnerability, monitor for unusually high CPU usage on systems using Bouncy Castle C# library versions 2.6.2 or earlier. Check for incoming CMP or CRMF messages with excessive iteration counts in PBMParameter fields. Use network traffic analysis tools to inspect message contents for abnormally large iteration values.

Impact Analysis

This vulnerability can impact systems using affected BC C# versions (2.6.2 and earlier) that verify messages from untrusted sources. Attackers can send specially crafted messages to consume excessive CPU resources, leading to service slowdowns or crashes. Servers like Certificate Authorities or Registration Authorities are particularly at risk.

Mitigation Strategies
  • Upgrade to Bouncy Castle C# library version 2.7.0 or later to enforce default iteration limits.
  • If upgrading is not possible, explicitly set a maximum iteration count in PKMacBuilder constructors.
  • Validate and reject incoming messages with iteration counts exceeding safe thresholds before processing.
  • Restrict network access to systems handling CMP/CRMF messages to trusted sources only.

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