Improper Integrity Check in AES-CCM Implementation of Bouncy Castle's C# Library
CVE-2026-15999

8.2HIGH

Key Information:

Vendor

Legion Of The Bouncy Castle Inc.

Status
Bc-csharp
Vendor
CVE Published:
2 October 2026

What is CVE-2026-15999?

The Bouncy Castle C# library contains a vulnerability that arises from improper validation of integrity check values in its AES-CCM implementation. This flaw allows an adversary to intercept and manipulate CCM-encrypted data without detection by exploiting the AlgorithmIdentifier, especially when the authentication tag length is either set to zero or is incorrectly defined outside the specified RFC 5084 parameters. The lack of strict validation within CcmParameters, combined with the vulnerability in CcmBlockCipher that validates tag length solely during encryption, permits the decryption process to erroneously accept short or zero-length tags during checks, affecting various components including ParameterUtilities.GetCipherParameters and CmsEnvelopedData.

Affected Version(s)

bc-csharp 0 < 2.7.0

References

https://github.com/bcgit/bc-csharp/wiki/CVE-2026-15999
vendor-advisory
https://github.com/bcgit/bc-csharp/commit/2818bdfa55efd58...
patch
https://github.com/bcgit/bc-csharp/commit/9d284d8f379614d...
patch

CVSS V4

Score:
8.2
Severity:
HIGH
Confidentiality:
None
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
Physical
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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