Is CVE-2026-63577 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-63577 being exploited in the wild.

How severe is CVE-2026-63577?

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-2026-63577?

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-2026-63577 attacked?

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

Am I affected by CVE-2026-63577?

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-2026-63577: Bouncy Castle improper certificate name-constraint validation

CVE-2026-63577 · Severity: info · Published 2026-10-02

Bouncy Castle is a cryptography library used to validate X.509 digital certificates in enterprise applications. A flaw in its name-constraint validation allows an attacker who controls an intermediate certificate authority to issue certificates that bypass security checks, potentially enabling unauthorized certificate acceptance in certificate chain validation and trust decisions.

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

Quick answers

Is CVE-2026-63577 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-63577 being exploited in the wild.
How severe is CVE-2026-63577?: 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-2026-63577?: 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-2026-63577 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-63577?: 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.WithinDNSubtree method in Bouncy Castle before 2.7.0 improperly validates directoryName name-constraints by searching for the constraint's first RDN anywhere in a certificate's distinguished name rather than requiring it to be an initial prefix, violating RFC 5280. An attacker with a name-constrained intermediate CA can craft certificates whose subject DN or directoryName subjectAltName falls outside the permitted subtrees but passes validation. The fix requires matching RFC 5280 compliance for initial prefix checking.

Affected products

Legion of the Bouncy Castle BouncyCastle.Cryptography before 2.7.0

Timeline

2026-10-02: disclosed
2026-07-01: patched

References

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