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

published 2026-10-02 38 d ago modified 2026-10-28 11 d ago also EUVD-2026-91232

cvss: 5.3; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 14%
public exploits: 0; none known

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.

Patch / fix

fixed in 1 links 4

Legion of the Bouncy Castle Inc. bc-csharp 2.7.0

github.com/bcgit/bc-csharp@f196a22 commit
github.com/bcgit/bc-csharp@be276e0 commit
github.com/bcgit/bc-csharp@75c3c57 commit
github.com/bcgit/bc-csharp/wiki/CVE-2026-103602 advisory

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 37 d ago (2026-10-02)

Exploit prediction

0.23% chance of exploitation in the next 30 days, higher than 14% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	4.0	8.2	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
CNA	4.0	8.2	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD	3.1	5.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Affected products

Legion of the Bouncy Castle Inc. bc-csharp

Classification

Weakness

CWE-295 Improper Certificate Validation

References

Sources

CVE List CVE-2026-103602
NVD CVE-2026-103602

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary