CVE-2026-63577Hinoki check available

Certificate constraint bypass via non-prefix DN matching

Published Oct 2, 2026 · Updated Oct 2, 2026

Improper certificate validation in Bouncy Castle C# API before 2.7.0 allows attackers to bypass directoryName constraints in PKIX paths. PkixNameConstraintValidator.WithinDNSubtree accepts a permitted RDN sequence found after other RDNs rather than requiring that sequence at the start of the name. Exploitation requires control of, or certificate issuance by, a name-constrained intermediate CA and an application that relies on the affected PKIX validation.

CVSS severityUnavailable
Unscored
EPSS probability0.24%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Improper certificate validation in Bouncy Castle C# API before 2.7.0 allows attackers to bypass directoryName constraints in PKIX paths. PkixNameConstraintValidator.WithinDNSubtree accepts a permitted RDN sequence found after other RDNs rather than requiring that sequence at the start of the name. Exploitation requires control of, or certificate issuance by, a name-constrained intermediate CA and an application that relies on the affected PKIX validation.

The record

CVE
CVE-2026-63577
Published
Oct 2, 2026
Updated
Oct 2, 2026
Vendor
Legion of the Bouncy Castle Inc.
Product
Bouncy Castle C# API
Classifications
Unavailable
Attack vector
Unavailable
Privileges
Unavailable

Timeline

How it unfolded

  1. Oct 2, 2026CVE publishedPublication date reported by the CVE source.
  2. Oct 2, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <2.7.0

What conditions does exploitation require?

Attack vectorUnavailable in this record.
Required privilegesUnavailable in this record.

What is affected?

Legion of the Bouncy Castle Inc. · Bouncy Castle C# APIversion=0 <2.7.0

Published CVSS scores

No CVSS assessment is available in this record.

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
VectorUnavailable
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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