High · CVSS 8.2CVE-2026-63576

URI name constraints checked against a mis-parsed host

Answer in brief

CVE-2026-63576 records a High severity (CVSS 8.2) vulnerability in URI name constraints checked against a mis-parsed host. The current sources do not mark it as known exploited. The current feed maps Legion of the Bouncy Castle Inc./BouncyCastle.Cryptography (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 2, 2026Updated Oct 2, 2026Source checked Oct 2, 2026First seen by HOL Oct 2, 2026Material review Oct 2, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 8.2
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 8.2. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Legion of the Bouncy Castle Inc./BouncyCastle.Cryptography (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Legion of the Bouncy Castle Inc./BouncyCastle.Cryptographygeneric	>=0 <2.7.0	2.7.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for Legion of the Bouncy Castle Inc./BouncyCastle.Cryptography.
Review the reported fix. Update Legion of the Bouncy Castle Inc./BouncyCastle.Cryptography to 2.7.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Oct 2, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 2, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Oct 2, 2026

Sources and claim methodology

Upstream source description

Improper certificate validation in PkixNameConstraintValidator (ExtractHostFromURL) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a name-constrained subordinate CA, or anyone able to obtain certificates with chosen subjectAltName URIs from such a CA, to bypass permitted or excluded uniformResourceIdentifier name constraints during certification path validation via a URI whose path, query, fragment or userinfo contains characters such as '@' or ':', because the host was extracted by string slicing without first isolating the RFC 3986 authority component, so the host compared against the constraints could differ from the URI's actual host.

Quoted source text, attributed separately from HOL analysis.