CVE-2026-63576: Improper certificate validation in PkixNameConstraintValidator (ExtractHostFromURL) in Legion of the Bouncy Ca

Q: How do I fix CVE-2026-63576?

bc-csharp: upgrade to 2.7.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-63576 being exploited?

CVE-2026-63576 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-63576 affect?

CVE-2026-63576 affects bc-csharp. Severity is high (CVSS 7.5). 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 subje

Q: How urgent is CVE-2026-63576?

Priority 36/100. High severity; Remotely exploitable, no login, no user action

Routine

HIGH 7.5REMOTEUPGRADE

CVE-2026-63576 is a high-severity flaw (CVSS 7.5) affecting bc-csharp. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 characte

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 82%)
CISA exploited list	No
Weakness	CWE-295
Published	2026-10-02
Last modified	2026-10-28

Publisher (CNA): bcorg · Vendor: bouncycastle

Last updated 2026-10-28 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-10-02 08:17 UTCPublished CVE record published
2026-10-28 14:38 UTCUpdated Record last modified

bouncycastle bc-csharp UPGRADE

Affected: < 2.7.0

Fixed in: 2.7.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy bc-csharp || rpm -q bc-csharp || bc-csharp --version

2. UPGRADE to 2.7.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade bc-csharp

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade bc-csharp

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-63576?

bc-csharp: upgrade to 2.7.0. Exact commands for each OS are on this page.

Is CVE-2026-63576 being exploited?

CVE-2026-63576 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-63576 affect?

CVE-2026-63576 affects bc-csharp. Severity is high (CVSS 7.5). 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 subje

How urgent is CVE-2026-63576?

Priority 36/100. High severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-63569 MEDIUM 6.5 UPGRADE Improper input validation in DHAgreement.CalculateAgreement (MTI/A0 two-pass Diffie-Hellman) in Legion of the
CVE-2026-103600 HIGH 7.5 UPGRADE Uncontrolled recursion in the ASN.1 parser (Asn1InputStream, Asn1StreamParser) in Legion of the Bouncy Castle
CVE-2026-103601 HIGH 7.5 UPGRADE Release of unverified plaintext in the CCM (CcmBlockCipher) and DSTU 7624 CCM (KCcmBlockCipher) AEAD modes in
CVE-2026-63575 HIGH 7.5 UPGRADE Loop with unreachable exit condition in the PKCS#12 key derivation (Pkcs12ParametersGenerator) in Legion of th
CVE-2026-63577 HIGH 7.5 UPGRADE Improper certificate validation in the directoryName name-constraint check (PkixNameConstraintValidator.Within

References

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