Is CVE-2026-63576 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-63576 being exploited in the wild.

How severe is CVE-2026-63576?

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-2026-63576?

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-2026-63576 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-63576?

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-2026-63576: Bouncy Castle C# improper certificate validation in URI name constraints

CVE-2026-63576 · Severity: info · Published 2026-10-02

Bouncy Castle C# is a cryptography library used to validate X.509 digital certificates. This vulnerability allows attackers with access to a subordinate Certificate Authority to bypass name constraints by crafting URIs with special characters, potentially enabling them to impersonate legitimate domains and compromise certificate-based security checks.

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

Quick answers

Is CVE-2026-63576 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-63576 being exploited in the wild.
How severe is CVE-2026-63576?: 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-2026-63576?: 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-2026-63576 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-63576?: 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 PkixNameConstraintValidator's ExtractHostFromURL function improperly parses URIs by using string slicing without first isolating the RFC 3986 authority component, allowing characters like '@' or ':' in the URI's path, query, fragment, or userinfo to cause the extracted hostname to differ from the actual host. This enables bypassing of uniformResourceIdentifier name constraints during certification path validation. A name-constrained subordinate CA can obtain certificates with crafted subjectAltName URIs to exploit this parsing flaw.

Affected products

Legion of the Bouncy Castle BouncyCastle.Cryptography before 2.7.0

Timeline

2026-07-02: patched
2026-10-02: advisory

References

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