PatchTheCVECVE-2026-103602: Improper certificate validation in PkixNameConstraintValidator in Legion of the Bouncy Castle Inc
CVE-2026-103602 is a medium-severity flaw (CVSS 5.3) affecting bc-csharp. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
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
Why this priority
- Remotely exploitable, no login, no user action
A fixed release or distro patch exists.
Risk facts
| CVSS score | 5.3 (Medium) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 0.3% (top 79%) |
| CISA exploited list | No |
| Weakness | CWE-295 |
| Published | 2026-10-02 |
| Last modified | 2026-10-28 |
Last updated 2026-10-28 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2026-103602?
bc-csharp: upgrade to 2.7.0. Exact commands for each OS are on this page.
Is CVE-2026-103602 being exploited?
CVE-2026-103602 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2026-103602 affect?
CVE-2026-103602 affects bc-csharp. Severity is medium (CVSS 5.3). 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 certifica
How urgent is CVE-2026-103602?
Priority 29/100. Remotely exploitable, no login, no user action
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