FreeRDP HTTP Proxy CONNECT Request Injection via RDP Redirection PDU

Technical Analysis

The vulnerability (CVE-2026-67289) resides in http_proxy_connect() within FreeRDP's client proxy-connection logic, where the ServerHostname value—derived unsanitized from the server-supplied TargetNetAddress redirection field—is concatenated directly into the CONNECT request line and Host header. Because CRLF and other control characters are not filtered, an attacker controlling or spoofing an RDP server can craft a redirection PDU that injects additional HTTP headers or entirely separate requests into the proxy tunnel, a classic CRLF/HTTP request-smuggling primitive that can lead to proxy cache poisoning, credential relay, SSRF-like pivoting, or bypass of proxy access controls. The flaw requires no client-side interaction beyond initiating an RDP session redirect, and combined with the 9.8 CVSS score, indicates trivial exploitability with high confidentiality/integrity/availability impact. Enterprises running FreeRDP-based clients or headless automation (e.g., jump hosts, bastion RDP gateways, or CI/CD infrastructure) that route RDP sessions through corporate HTTP proxies are directly exposed. Where AI agent orchestration systems use FreeRDP-based remote desktop clients or automation frameworks to control remote Windows hosts through proxied network paths, this flaw could allow attackers to hijack or manipulate the agent's outbound HTTP proxy tunnel, potentially exfiltrating credentials or injecting malicious responses into agent-driven RDP automation workflows.

Affected Systems

FreeRDP versions <= 3.28.0 (all client builds using http_proxy_connect() for RDP session redirection through HTTP proxies); patched in FreeRDP 3.29.0. Affects Linux, macOS, and Windows FreeRDP client installations, including embedded uses in remote access tools, VDI clients, and automation/orchestration platforms that rely on FreeRDP libraries.

Indicators of Compromise

• No specific malware hashes, IPs, or domains published — exploitation is via crafted RDP Redirection PDU (TargetNetAddress field containing CRLF/control characters)
• Watch for anomalous HTTP CONNECT requests containing unexpected headers or multiple request lines originating from RDP client hosts
• Unexpected proxy log entries with malformed Host headers tied to RDP client processes

Remediation Steps

1. 1

   Upgrade FreeRDP

   Update all FreeRDP client installations and any dependent applications/libraries to version 3.29.0 or later, which validates and rejects control characters in the TargetNetAddress redirection field.

2. 2

   Restrict RDP Server Trust

   Only connect to RDP servers from trusted, authenticated sources; disable or restrict RDP session redirection features where not required.

3. 3

   Proxy-Side Validation

   Configure HTTP proxies to reject CONNECT requests containing malformed headers, embedded CRLF sequences, or multiple request lines as a defense-in-depth measure.

4. 4

   Network Segmentation

   Isolate RDP client hosts and jump servers from sensitive internal proxy infrastructure, and monitor proxy logs for anomalous CONNECT traffic patterns.

5. 5

   Audit Automation Pipelines

   Review any AI agent, automation, or orchestration systems that use FreeRDP-based remote desktop clients through proxied connections, and patch or isolate them to prevent credential exposure or request injection.