CVE-2026-63576 Legion of the Bouncy Castle Inc. bc-csharp - Authentication Bypass

Legion of the Bouncy Castle Inc. bc-csharp < 2.7.0 contains an improper certificate validation caused by incorrect host extraction in PkixNameConstraintValidator, letting attackers bypass URI name constraints during certification path validation, exploit requires crafted certificates with specific subjectAltName URIs.

CVSS base score 8.2 /10
High
CISA KEV
Not listed
Public exploit
None known
Authentication
Not required
EPSS
0.22% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
Authentication Bypass
Impact
Broken Authentication
CVSS vector
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
Published
2 October 2026
Updated
15 October 2026
Weakness
CWE-295

Vendor fix

Upgrade to version 2.7.0 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

References

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