Bug 2510026 (CVE-2026-66402)

Summary: CVE-2026-66402 FreeRDP: FreeRDP: Server Identity Verification Bypass via TLS Certificate Validation Weaknesses
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in FreeRDP. This flaw involves multiple weaknesses in how FreeRDP validates TLS (Transport Layer Security) certificates. FreeRDP's custom validation logic can incorrectly process DNS Subject Alternative Name (SAN) values, accept Common Names without proper comparison to other SAN entries, and fail to validate IP address SANs for IP-literal targets. An attacker, by presenting a specially crafted certificate, could exploit these weaknesses to bypass server identity verification, potentially allowing them to impersonate a legitimate server and compromise the security of the connection.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On: 2510318, 2510319    
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Description OSIDB Bzimport 2026-08-01 13:04:00 UTC 
FreeRDP before 3.29.0 (affected versions <= 3.28.0) contains multiple TLS certificate identity validation weaknesses in tls_verify_certificate(), tls_match_hostname(), and x509_utils_get_dns_names(). Because FreeRDP performs custom Common Name and DNS SAN string matching instead of using OpenSSL's length-aware identity validation APIs, it (1) truncates DNS SAN values at embedded NUL bytes (accepting e.g. 'victim.example\0.attacker.example' as 'victim.example'), (2) accepts a matching Common Name even when non-matching DNS SAN entries are present, and (3) accepts IP-literal targets via DNS/CN matching without comparing iPAddress SANs. Under a trusted or misissued certificate chain, an attacker positioned to present such a certificate can bypass server identity verification, weakening TLS server authentication.