Name Constraints bypass: directoryName constraint matched at any position in the DN instead of as a prefix
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- Present
- Impact type
- Spoofing
- Confidentiality · integrity · availability
- None · High · None
- Fix status
- Fixed
Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-295.
Summary
Improper certificate validation in the directoryName name-constraint check (PkixNameConstraintValidator.WithinDNSubtree) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows an attacker who controls, or can have certificates issued by, a name-constrained intermediate CA to get certificates accepted by PKIX path validation whose subject distinguished name, or a directoryName subjectAltName, lies outside the CA's permitted subtrees, via a name that places other RDNs ahead of a copy of the permitted RDN sequence, because the check looks for the constraint's first RDN anywhere in the name and compares the remaining RDNs from that position, instead of requiring the constraint to be an initial prefix of the name as RFC 5280 sections 4.2.1.10 and 7.1 require.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Legion of the Bouncy Castle Inc. | bc-csharp | before 2.7.0 | 2.7.0 | Patch available | CNA |
- bc-csharp VendorLegion of the Bouncy Castle Inc. Affected before 2.7.0 Fixed in 2.7.0 Patch available CNA
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:bouncycastle:bc-csharp:*:*:*:*:*:*:*:* | before 2.7.0 | Vulnerable | Legion of the Bouncy Castle Inc. |
- cpe:2.3:a:bouncycastle:bc-csharp:*:*:*:*:*:*:*:* Versions before 2.7.0 Vulnerable ·Legion of the Bouncy Castle Inc.
Remediation
- Fix · CNA bc-csharp (Legion of the Bouncy Castle Inc.) Fixed in 2.7.0
Fixed in the same release
Records fixed by the same vendor advisory or release, as the CNA lists them.
- Release ·
Legion of the Bouncy Castle bc-csharp 2.7.0
21 records Highest priority Priority MEDIUM 8 MEDIUM, 13 LOW
Other records, highest priority first
- TI-2026-65844 MTI/A0 DHAgreement does not validate the peer's ephemeral valuePriority MEDIUM 47
- TI-2026-66020 Unbounded HSS public key level count allows huge array allocation during signature verificationPriority MEDIUM 44
- TI-2026-66017 Unbounded ASN.1 nesting depth causes process-terminating stack overflowPriority MEDIUM 44
Timeline
- 2026-10-02 Threatist record created from CVE-2026-63577
- 2026-10-03 Alias added: GHSA-437r-hr8h-5f45
- 2026-10-06 CISA SSVC decision points changed
- 2026-10-28 CVSS score added · NVD
References
More Legion of the Bouncy Castle Inc. Bc-csharp vulnerabilities
- TI-2026-65844 MTI/A0 DHAgreement does not validate the peer's ephemeral value CVSS 4.0CRITICAL 9.1
- TI-2026-66020 Unbounded HSS public key level count allows huge array allocation during signature verification CVSS 4.0HIGH 8.7
- TI-2026-66017 Unbounded ASN.1 nesting depth causes process-terminating stack overflow CVSS 4.0HIGH 8.7
- TI-2026-65849 Unbounded allocation from OpenPGP signature and user attribute subpacket lengths CVSS 4.0HIGH 8.7
- TI-2026-65843 Unbounded CMP/CRMF password-based MAC iteration count allows CPU exhaustion CVSS 4.0HIGH 8.7
- TI-2026-65841 DTLS handshake reassembler allocates buffer from unchecked 24-bit length CVSS 4.0HIGH 8.7
Sources
- CVE-2026-63577 · CVE Program
- CVE-2026-63577 · NVD
- FIRST EPSS
- GHSA-437r-hr8h-5f45 · GitHub Advisory Database · CC BY 4.0
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