CVE-2026-32624: xrdp Buffer Overflow Vulnerability

CVE-2026-32624 Overview

CVE-2026-32624 is a heap-based buffer overflow vulnerability affecting xrdp, an open source Remote Desktop Protocol (RDP) server. The vulnerability exists in the logon processing functionality and can be triggered by unauthenticated remote attackers when the domain_user_separator directive is explicitly configured in xrdp.ini. By sending a crafted, excessively long username and domain name combination, an attacker can overflow the internal buffer and corrupt adjacent memory regions.

Critical Impact

Unauthenticated remote attackers can trigger a Denial of Service (DoS) condition or cause unexpected behavior on xrdp servers with non-default domain_user_separator configuration.

Affected Products

• xrdp versions through 0.10.5
• Systems with domain_user_separator configured in xrdp.ini
• Linux/Unix servers running xrdp as an RDP gateway

Discovery Timeline

• 2026-04-17 - CVE CVE-2026-32624 published to NVD
• 2026-04-20 - Last updated in NVD database

Technical Details for CVE-2026-32624

Vulnerability Analysis

This vulnerability is classified as CWE-122 (Heap-based Buffer Overflow), a memory corruption flaw that occurs when data written to a heap-allocated buffer exceeds its allocated size. The vulnerability resides in xrdp's logon processing code path, which handles username and domain name parsing during RDP authentication.

The flaw is only exploitable when the domain_user_separator directive is explicitly configured in the xrdp.ini configuration file. By default, this directive is commented out, meaning default installations are not vulnerable. However, organizations that have enabled this feature to support domain-based authentication are at risk.

An unauthenticated attacker with network access to the xrdp service (typically TCP port 3389) can exploit this vulnerability without requiring valid credentials. The attack involves sending malformed RDP logon packets containing oversized username and domain fields that exceed the expected buffer boundaries.

Root Cause

The root cause is insufficient bounds checking when processing username and domain name strings during logon authentication. When domain_user_separator is configured, xrdp concatenates the domain and username into an internal buffer without properly validating that the combined length does not exceed the allocated buffer size. This allows an attacker to provide excessively long input that overflows the heap-allocated buffer and corrupts adjacent memory regions.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can remotely target any xrdp server that has domain_user_separator enabled by connecting to the RDP port and initiating a malicious logon sequence. The crafted packet contains an oversized username and domain combination designed to trigger the heap overflow during the parsing phase of authentication processing.

The vulnerability can be exploited to cause a Denial of Service by crashing the xrdp service or inducing unexpected behavior through memory corruption. Due to the nature of heap overflows, exploitation beyond DoS may be theoretically possible depending on memory layout and heap allocator behavior, though no public exploits demonstrating such capabilities have been identified.

Detection Methods for CVE-2026-32624

Indicators of Compromise

• Unexpected xrdp service crashes or restarts, particularly during authentication attempts
• Anomalous RDP logon attempts with unusually long username or domain fields in authentication logs
• Memory corruption errors or segmentation faults in xrdp process logs
• Increased connection attempts to RDP ports from unknown sources

Detection Strategies

• Monitor xrdp logs for authentication failures with malformed or excessively long usernames
• Implement network intrusion detection rules to identify RDP packets with oversized credential fields
• Deploy endpoint detection solutions capable of identifying heap corruption and abnormal process termination
• Review system logs for repeated xrdp service failures or unexpected terminations

Monitoring Recommendations

• Enable detailed logging in xrdp to capture authentication attempt details
• Configure alerting for xrdp service crashes or high restart rates
• Implement network traffic analysis to detect anomalous RDP traffic patterns
• Monitor for connections to RDP services from unexpected geographic regions or IP ranges

How to Mitigate CVE-2026-32624

Immediate Actions Required

• Upgrade xrdp to version 0.10.6 or later immediately
• If upgrade is not immediately possible, comment out or remove the domain_user_separator directive from xrdp.ini
• Restrict network access to xrdp services using firewall rules to limit exposure
• Implement network segmentation to isolate RDP servers from untrusted networks

Patch Information

The vulnerability has been fixed in xrdp version 0.10.6. Organizations should upgrade to this version or later to fully remediate the issue. The patch addresses the buffer overflow by implementing proper bounds checking when processing username and domain name strings during logon.

For detailed information about the fix, refer to the GitHub Release v0.10.6 and the GitHub Security Advisory GHSA-7q2g-6fjr-h6pp.

Workarounds

• Comment out the domain_user_separator directive in xrdp.ini to revert to default (non-vulnerable) behavior
• Implement a VPN or jump host requirement to access xrdp services, reducing external attack surface
• Deploy a Web Application Firewall (WAF) or network security device capable of inspecting RDP traffic for malicious patterns
• Limit RDP access to known, trusted IP addresses through firewall ACLs

# Configuration example
# In /etc/xrdp/xrdp.ini, ensure domain_user_separator is commented out:
# domain_user_separator=@

# Alternatively, restrict access via iptables:
iptables -A INPUT -p tcp --dport 3389 -s <trusted_network> -j ACCEPT
iptables -A INPUT -p tcp --dport 3389 -j DROP