CVE-2026-121392
Description
A flaw was found in FreeRDP. A man-in-the-middle attacker possessing a certificate issued by a trusted Certificate Authority (CA) can exploit improper certificate identity validation during connection establishment. Because the client incorrectly accepts fallback certificate names and improperly validates IP addresses, server identity verification can be bypassed. Consequently, an attacker can intercept Remote Desktop Protocol (RDP) sessions to view and capture sensitive data, including screen displays, keystrokes, and clipboard contents.
Statement
An improper certificate validation vulnerability was discovered in FreeRDP's tls_verify_certificate() function where fallback Common Name parsing is accepted despite non-matching Subject Alternative Names (SAN) and IP literals are matched against DNS strings. A man-in-the-middle attacker holding a certificate signed by any client-trusted CA can bypass server identity verification to intercept and tamper with RDP session traffic, capturing sensitive screen contents, keystrokes, and clipboard data.
Mitigation
Enforce strict pre-configured server public key pinning or restrict trusted root Certificate Authorities within the client environment to prevent acceptance of rogue certificates issued by untrusted or compromised CAs. Where possible, tunnel RDP connections through an authenticated VPN or IPsec tunnel to verify endpoint identity independently of TLS certificate validation.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.4 | N/A | 7.4 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | High | N/A | High |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Understanding the Weakness (CWE)
Integrity,Authentication
Technical Impact: Bypass Protection Mechanism; Gain Privileges or Assume Identity
When a certificate is invalid or malicious, it might allow an attacker to spoof a trusted entity by interfering in the communication path between the host and client. The product might connect to a malicious host while believing it is a trusted host, or the product might be deceived into accepting spoofed data that appears to originate from a trusted host.
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