CVE-2025-68118: FreeRDP Use-After-Free Vulnerability

CVE-2025-68118 Overview

CVE-2025-68118 is an Out-of-Bounds Read vulnerability in FreeRDP, a free implementation of the Remote Desktop Protocol. The vulnerability exists in FreeRDP's certificate handling code on Windows platforms, specifically in the freerdp_certificate_data_hash function which uses the Microsoft-specific _snprintf function to format certificate cache filenames. When truncation occurs, _snprintf does not append a terminating NUL byte if the formatted output exceeds the destination buffer size, potentially leading to memory disclosure or client crashes.

Critical Impact

An attacker controlling the hostname value (via server redirection or crafted .rdp file) can cause a heap-based out-of-bounds read, potentially exposing sensitive memory contents or causing denial of service through client crashes.

Affected Products

• FreeRDP versions prior to 3.20.0
• Windows platform deployments of FreeRDP
• Applications utilizing FreeRDP certificate handling functions

Discovery Timeline

• 2025-12-17 - CVE-2025-68118 published to NVD
• 2026-01-02 - Last updated in NVD database

Technical Details for CVE-2025-68118

Vulnerability Analysis

This vulnerability is classified as CWE-125 (Out-of-bounds Read). The flaw resides in FreeRDP's certificate data handling mechanism on Windows platforms. The root issue stems from improper use of the _snprintf function when generating certificate cache filenames. Unlike standard snprintf, the Microsoft _snprintf function does not guarantee NUL termination when the output is truncated to fit within the buffer size.

When processing certificate data, if an attacker can influence the hostname value through mechanisms such as RDP server redirection or by crafting a malicious .rdp file, they can trigger a condition where the resulting filename buffer lacks proper NUL termination. Subsequent string operations on this non-terminated buffer will continue reading beyond allocated memory boundaries, resulting in a heap-based out-of-bounds read condition.

While the default configuration typically terminates the connection before significant data exposure occurs, the vulnerability can still result in unintended memory reads or client crashes under specific conditions, representing a denial of service risk with potential for information disclosure.

Root Cause

The root cause is the use of Microsoft's _snprintf function without proper handling of buffer truncation scenarios. According to Microsoft documentation, _snprintf does not append a terminating NUL byte when the formatted output exceeds the destination buffer size. The vulnerable code path in libfreerdp/crypto/certificate_data.c failed to account for this behavior, leaving buffers potentially unterminated after truncation.

Attack Vector

This vulnerability is exploitable over the network without requiring authentication or user interaction. An attacker can exploit this vulnerability through:

1. Server Redirection Attack: A malicious or compromised RDP server can redirect the client to a hostname crafted to trigger buffer truncation
2. Malicious RDP File: An attacker can craft an .rdp configuration file with an excessively long hostname that triggers the vulnerable code path when opened by a victim

The attack requires the victim to connect to an attacker-controlled server or open a malicious .rdp file.

 #include <freerdp/crypto/certificate_data.h>
 
 #include "certificate.h"
+#include <freerdp/log.h>
+#define TAG FREERDP_TAG("crypto.certificate_data")
 
 struct rdp_certificate_data
 {

Source: GitHub Commit Update

The patch adds proper logging capabilities and implements additional certificate data validation checks to ensure proper buffer handling.

Detection Methods for CVE-2025-68118

Indicators of Compromise

• Unexpected FreeRDP client crashes when connecting to unfamiliar RDP servers
• Receipt of .rdp files with unusually long hostnames or suspicious connection parameters
• Connection attempts to RDP servers with abnormally long hostnames in network logs
• Memory access violations in freerdp_certificate_data_hash or related certificate functions

Detection Strategies

• Monitor for FreeRDP client crash events or access violations related to certificate handling
• Implement network monitoring to detect RDP connections to suspicious or newly registered domains
• Use endpoint detection to identify malicious .rdp file execution with anomalous parameters
• Deploy application-level monitoring for string operations on certificate-related buffers

Monitoring Recommendations

• Enable crash reporting and analysis for FreeRDP client applications
• Monitor network traffic for RDP server redirections to unexpected destinations
• Implement file system monitoring for .rdp file creation and modification in user-accessible directories
• Review RDP connection logs for connections to hosts with unusually long names

How to Mitigate CVE-2025-68118

Immediate Actions Required

• Upgrade FreeRDP to version 3.20.0 or later immediately
• Review and restrict sources of .rdp files users can open
• Implement network-level controls to limit RDP connections to trusted servers only
• Consider temporarily disabling RDP redirection features until patching is complete

Patch Information

FreeRDP has released version 3.20.0 which addresses this vulnerability. The fix implements proper buffer termination handling in the certificate data processing code. The security patch can be reviewed in the GitHub Commit. Additional details are available in the GitHub Security Advisory GHSA-h78c-5cjx-jw6x.

Workarounds

• Block or quarantine suspicious .rdp files at email gateways and file transfer points
• Implement application whitelisting to control which RDP clients can execute
• Use network segmentation to limit RDP connectivity to approved server destinations
• Educate users about the risks of opening .rdp files from untrusted sources

# Configuration example - Restrict RDP connections to trusted hosts
# Add to firewall rules or network policy
iptables -A OUTPUT -p tcp --dport 3389 -d trusted.rdp.server.com -j ACCEPT
iptables -A OUTPUT -p tcp --dport 3389 -j DROP