CVE-2026-63577 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 vulnerability caused by incorrect directoryName name-constraint checks in PkixNameConstraintValidator.WithinDNSubtree, letting attackers with control over name-constrained intermediate CAs bypass PKIX path validation, exploit requires attacker to control or have certificates issued by a name-constrained intermediate CA.

CVSS base score 8.2 /10
High
CISA KEV
Not listed
Public exploit
None known
EPSS
0.24% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
Authentication Bypass
Impact
Privilege Escalation
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

Update 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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