---
title: "CVE-2026-63577: Legion of the Bouncy Castle Inc. bc-csharp - Authentication Bypass"
description: "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."
url: https://panop.io/threat-heartbeat/CVE-2026-63577/
---

# 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 ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-63577)

## 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](https://cwe.mitre.org/data/definitions/295.html)

## 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

- [https://nvd.nist.gov/vuln/detail/CVE-2026-63577](https://nvd.nist.gov/vuln/detail/CVE-2026-63577)
- [https://github.com/bcgit/bc-csharp/commit/606e9153b97a265c70ca8293d21ec859344d7de8](https://github.com/bcgit/bc-csharp/commit/606e9153b97a265c70ca8293d21ec859344d7de8)
- [https://github.com/bcgit/bc-csharp/commit/75c3c576602886180ed92a63c89419e3bd63b392](https://github.com/bcgit/bc-csharp/commit/75c3c576602886180ed92a63c89419e3bd63b392)
- [https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63577](https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63577)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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