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Advisory details: gitlab / maven/org.bouncycastle/bctls-jdk18on/CVE-2026-59638
Advisory ID gitlab/maven/org.bouncycastle/bctls-jdk18on/CVE-2026-59638
Aliases CVE-2026-59638
Summary JSSE hostname verifier CN-fallback enabled by default despite documented opt-in Affects Bouncy Castle for Java before 1.85. HostnameUtil gates the fallback that matches the certificate CN when no dNSName SAN is present on a property whose unset default the code treats as enabled, contrary to its documentation. Because name-constraint processing only constrains SAN entries of the constrained type, a leaf with no dNSName SAN passes a dNSName-constrained chain, and the verifier then matches the attacker-chosen CN against the target hostname.
Status Published
Exploitability 0.5
Weighted Severity 0.0
Risk
Affected and Fixed Packages Package Details
Introduced and Fixed Package Commit Patches Package Commit Patches Details
Weaknesses (3)
CWE-297 Improper Validation of Certificate with Host Mismatch
CWE-937 OWASP Top Ten 2013 Category A9 - Using Components with Known Vulnerabilities
CWE-1035 OWASP Top Ten 2017 Category A9 - Using Components with Known Vulnerabilities
System Score Found at
cvssv3.1 https://gitlab.com/gitlab-org/advisories-community/-/blob/main/maven/org.bouncycastle/bctls-jdk18on/CVE-2026-59638.yml
Reference id Reference type URL
5ac55351cd1a8a7184d41c96a7ee87df0770240a Other https://github.com/bcgit/bc-java/commit/5ac55351cd1a8a7184d41c96a7ee87df0770240a
799bd15320a6310a447863638aa3df64acef829b Other https://github.com/bcgit/bc-java/commit/799bd15320a6310a447863638aa3df64acef829b
CVE-2026-59638 https://github.com/bcgit/bc-java/wiki/CVE-2026-59638
CVE-2026-59638 https://nvd.nist.gov/vuln/detail/CVE-2026-59638
No exploits are available.

No EPSS data available for this advisory.

Patch URL
There are no known patches.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N Found at https://gitlab.com/gitlab-org/advisories-community/-/blob/main/maven/org.bouncycastle/bctls-jdk18on/CVE-2026-59638.yml
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none

There are no SSVC decisions available.