Skip to main content

FreeRDP EUVDEUVD-2026-51851

| CVE-2026-66402 CRITICAL
Improper Certificate Validation (CWE-295)
2026-08-01 VulnCheck GHSA-759r-h698-g7xj
Authentication Bypass OpenSSL Freerdp
Critical
Disputed · 9.3 Vendor: VulnCheck
Share

Severity by source

Sources disagree (Medium–Critical)
Vendor (VulnCheck) PRIMARY
9.3 CRITICAL
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
6.8 MEDIUM

MITM position plus a trusted/misissued cert makes AC:H, a user must initiate the RDP connection (UI:R), and server-auth bypass enables full session interception (C:H/I:H) but not availability loss (A:N).

3.1 AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
4.0 AV:N/AC:H/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
SUSE
7.4 HIGH
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Red Hat
5.3 MEDIUM
qualitative

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorVendor: VulnCheck

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

3
Source Code Evidence Fetched
Aug 01, 2026 - 13:01 vuln.today
Analysis Generated
Aug 01, 2026 - 13:01 vuln.today
CVE Published
Aug 01, 2026 - 12:22 cve.org
CRITICAL 9.3

DescriptionCVE.org

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.

Articles & Coverage 1

News Critical TLS Certificate Verification Bypass in FreeRDP 3.x - CVE-2026-66402 Aug 01, 2026

AnalysisAI

TLS server-identity verification bypass in FreeRDP 3.x (all versions <= 3.28.0) lets a network attacker positioned between an RDP client and server defeat certificate hostname validation. Because tls_verify_certificate()/tls_match_hostname()/x509_utils_get_dns_names() perform custom Common Name and DNS SAN string matching instead of OpenSSL's length-aware identity APIs, NUL-truncated SAN values, CN acceptance despite non-matching SANs, and IP-literal matching without iPAddress SAN comparison all pass verification. Reported by VulnCheck with a vendor patch (3.29.0); no public exploit identified at time of analysis and it is not on CISA KEV.

Technical ContextAI

FreeRDP is the leading open-source Remote Desktop Protocol (RDP) client/library, embedded in tools like Remmina, xfreerdp/wlfreerdp, and numerous commercial VDI and remote-access products (CPE cpe:2.3:a:freerdp:freerdp:*). RDP secures its channel with TLS, and the client is responsible for confirming that the server certificate identifies the intended host. The root cause is CWE-295 (Improper Certificate Validation): rather than delegating to OpenSSL's length-aware identity routines (e.g. X509_check_host), FreeRDP re-implements matching over C strings, which mishandles embedded NUL bytes, treats a matching CN as sufficient even when DNS SAN entries contradict it, and matches IP-literal targets against DNS/CN fields without ever comparing the certificate's iPAddress SAN. Each is a classic identity-validation pitfall OpenSSL's native APIs are designed to avoid.

RemediationAI

Vendor-released patch: FreeRDP 3.29.0 - upgrade to 3.29.0 or later, which routes identity validation through OpenSSL's length-aware APIs; fix commit https://github.com/FreeRDP/FreeRDP/commit/b9533f07f98c25ed01c5f543b4d0ce73e120f5fd and advisory https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-43hh-p3vw-hfx3. Where immediate upgrade is impossible, reduce exposure to the MITM precondition: restrict RDP to trusted networks or tunnel it over a VPN/IPsec link so an attacker cannot intercept the TLS session (trade-off: added overhead and configuration), and prefer pinning the exact expected server certificate/thumbprint client-side instead of relying on hostname matching (trade-off: pins must rotate when the server cert changes). Tightening the client's trusted-CA set limits the 'trusted chain' avenue but does not stop a misissued-but-trusted certificate, so it is only partial. Rebuild and redeploy any downstream products that statically link FreeRDP once they ship a 3.29.0-based build.

More in OpenSSL

View all
CVE-2014-0160 HIGH POC
7.5 Apr 07

The (1) TLS and (2) DTLS implementations in OpenSSL 1.0.1 before 1.0.1g do not properly handle Heartbeat Extension packe
CVE-2014-0195 MEDIUM POC
6.8 Jun 05

The dtls1_reassemble_fragment function in d1_both.c in OpenSSL before 0.9.8za, 1.0.0 before 1.0.0m, and 1.0.1 before 1.0
CVE-2014-0224 HIGH POC
7.4 Jun 05

OpenSSL before 0.9.8za, 1.0.0 before 1.0.0m, and 1.0.1 before 1.0.1h does not properly restrict processing of ChangeCiph
CVE-2016-0800 MEDIUM POC
5.9 Mar 01

The SSLv2 protocol, as used in OpenSSL before 1.0.1s and 1.0.2 before 1.0.2g and other products, requires a server to se
CVE-2015-0204 MEDIUM POC
4.3 Jan 09

The ssl3_get_key_exchange function in s3_clnt.c in OpenSSL before 0.9.8zd, 1.0.0 before 1.0.0p, and 1.0.1 before 1.0.1k

CVE-2015-4000 LOW POC
3.7 May 21

The TLS protocol 1.2 and earlier, when a DHE_EXPORT ciphersuite is enabled on a server but not on a client, does not pro
CVE-2014-3566 LOW POC
3.4 Oct 15

The SSL protocol 3.0, as used in OpenSSL through 1.0.1i and other products, uses nondeterministic CBC padding, which mak
CVE-2016-2107 MEDIUM POC
5.9 May 05

The AES-NI implementation in OpenSSL before 1.0.1t and 1.0.2 before 1.0.2h does not consider memory allocation during a

CVE-2015-1793 MEDIUM POC
6.5 Jul 09

The X509_verify_cert function in crypto/x509/x509_vfy.c in OpenSSL 1.0.1n, 1.0.1o, 1.0.2b, and 1.0.2c does not properly

CVE-2022-3602 HIGH
7.5 Nov 01

A buffer overrun can be triggered in X.509 certificate verification, specifically in name constraint checking. Rated hig
CVE-2014-3470 MEDIUM
4.3 Jun 05

The ssl3_send_client_key_exchange function in s3_clnt.c in OpenSSL before 0.9.8za, 1.0.0 before 1.0.0m, and 1.0.1 before
CVE-2017-3730 HIGH POC
7.5 May 04

In OpenSSL 1.1.0 before 1.1.0d, if a malicious server supplies bad parameters for a DHE or ECDHE key exchange then this

Same weakness CWE-295 – Improper Certificate Validation

View all
CVE-2015-3152 MEDIUM POC
5.9
CVE-2026-85102 CRITICAL POC
9.8
CVE-2017-2800 CRITICAL POC
9.8
CVE-2014-1266 HIGH POC
7.4
CVE-2022-47758 CRITICAL POC
9.8
CVE-2025-68121 CRITICAL POC
10.0
CVE-2025-29331 CRITICAL POC
9.8
CVE-2025-32878 CRITICAL POC
9.8

Same technique Authentication Bypass

View all
CVE-2023-22515 CRITICAL POC
9.8
CVE-2012-4681 CRITICAL POC
9.8
CVE-2013-2465 CRITICAL POC
9.8
CVE-2011-3544 CRITICAL POC
9.8
CVE-2022-40684 CRITICAL POC
9.8
CVE-2025-61882 CRITICAL POC
9.8
CVE-2024-0012 CRITICAL POC
9.3
CVE-2023-46805 HIGH POC
8.2

Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Module for Package Hub 15 SP7 Affected
SUSE Linux Enterprise Module for Package Hub 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected

Share

EUVD-2026-51851 vulnerability details – vuln.today
Back

This site uses cookies essential for authentication and security. No tracking or analytics cookies are used. Privacy Policy