CVE-2026-103602 Name constraints bypass via trailing dot in rfc822Name, dNSName and URI hosts
Attackers can bypass certificate name constraints in Bouncy Castle C# by using trailing dots in hostnames, allowing unauthorized certificates to be accepted.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-103602?
CVE-2026-103602 is a high-severity vulnerability in Legion of the Bouncy Castle Inc. bc-csharp, published on 2 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Improper certificate validation in PkixNameConstraintValidator in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows an attacker who controls, or can obtain certificates from, a name-constrained intermediate CA to have certificates accepted during PKIX certification path validation for email addresses, DNS names or URI hosts that lie within excluded subtrees applying to that CA, via an rfc822Name, dNSName or uniformResourceIdentifier name whose host ends with a dot, because names and constraints were compared without first removing the RFC 1034 root-label trailing dot, so a fully qualified host name did not match an excluded subtree for the same host written without the dot.
Weakness: CWE-295
Which versions are affected by CVE-2026-103602?
It affects 1 product.
Products include Bouncycastle Bc-Csharp.
How do I fix CVE-2026-103602?
No fix has been published for CVE-2026-103602 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-103602 being exploited?
There is no known exploitation of CVE-2026-103602 in the wild and no public exploit code.
Other vulnerabilities in Legion of the Bouncy Castle Inc. bc-csharp
- CVE-2026-63569 MTI/A0 DHAgreement does not validate the peer's ephemeral value
- CVE-2026-103600 Unbounded ASN.1 nesting depth causes process-terminating stack overflow
- CVE-2026-103603 Unbounded HSS public key level count allows huge array allocation during signature verification
- CVE-2026-103604 Quadratic-time escaping when converting X.509 distinguished names to strings
- CVE-2026-16000 KCcmBlockCipher (DSTU 7624 CCM) tag not bound to nonce when no associated data is used
Sources
Also known as GHSA-mx2f-845p-2h26.