CVE-2026-103602

Name constraints bypass via trailing dot in rfc822Name, dNSName and URI hosts

MEDIUM
5.3
CVSS Score
Published: October 2, 2026 at 07:10 AM UTC
Updated: October 28, 2026 at 01:30 PM UTC
2 products affected across 2 vendorsBc CsharpBouncy Castle for C# (bc-csharp)

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Severity
MEDIUM5.3
Exploit prediction
EPSS 0.2%
SSVC
No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 2.7.0
Affected range stops below 2.7.0, so it looks safe — our inference, not a vendor statement

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
LOW
Integrity
NONE
Availability
NONE
Vector?

Quick Info

StatusANALYZED
CWE
CWE-295

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