Is CVE-2026-15999 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-15999 being exploited in the wild.

How severe is CVE-2026-15999?

Informational severity, published 2 October 2026.

Which products and versions are affected?

Legion of the Bouncy Castle BouncyCastle.Cryptography before 2.7.0.

Is there a fix for CVE-2026-15999?

Yes: fixed in BouncyCastle.Cryptography 2.7.0. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-15999 attacked?

It is attacked over the network.

Am I affected by CVE-2026-15999?

Check whether you run Legion of the Bouncy Castle BouncyCastle.Cryptography at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-15999: Bouncy Castle AES-CCM authentication tag validation bypass

CVE-2026-15999 · Severity: info · Published 2026-10-02

Bouncy Castle is a cryptography library used to implement secure communications and data protection in .NET applications. A flaw in its AES-CCM implementation allows an attacker positioned on the network to modify encrypted data without detection by declaring invalid authentication tag lengths, bypassing integrity checks that would normally reject tampering. Applications using Bouncy Castle for encrypted communications or CMS data could have their data silently corrupted or replaced without warning.

Technologies: Legion of the Bouncy Castle BouncyCastle.Cryptography. Vendors: Legion of the Bouncy Castle.

Quick answers

Is CVE-2026-15999 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-15999 being exploited in the wild.
How severe is CVE-2026-15999?: Informational severity, published 2 October 2026.
Which products and versions are affected?: Legion of the Bouncy Castle BouncyCastle.Cryptography before 2.7.0.
Is there a fix for CVE-2026-15999?: Yes: fixed in BouncyCastle.Cryptography 2.7.0. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-15999 attacked?: It is attacked over the network.
Am I affected by CVE-2026-15999?: Check whether you run Legion of the Bouncy Castle BouncyCastle.Cryptography at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

Fixed in: BouncyCastle.Cryptography 2.7.0

Technical details

The vulnerability is an improper validation flaw in CcmParameters and CcmBlockCipher that accepts any value for the authentication tag (ICV) length, including zero and values outside RFC 5084. The tag is only validated during encryption, not decryption, so an on-path attacker can replace CCM-encrypted content with a modified version claiming a zero-length or invalid tag length to bypass integrity checks. Affected code paths include ParameterUtilities.GetCipherParameters and CmsEnvelopedData/CmsEnvelopedDataParser for CCM-encrypted EnvelopedData.

Affected products

Legion of the Bouncy Castle BouncyCastle.Cryptography before 2.7.0

Timeline

2026-10-02: disclosed

References

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