CVE-2026-54538 in xrdp
Summary
by MITRE • 07/20/2026
xrdp is an open source RDP server. In versions 0.10.6 and prior, a n issue was discovered where the software fails to properly validate the totalLength field within the RDP protocol control header during packet reception. An unauthenticated remote attacker can exploit this vulnerability by sending a specially crafted packet that forces the xrdp process or thread into an infinite, CPU-bound loop. Because the internal pointer fails to advance and the deadlock prevention mechanism is bypassed for specific protocol data unit types, the process consumes excessive CPU resources indefinitely. This can render the xrdp service unavailable and potentially lead to system-wide resource exhaustion if multiple malicious connections are established. This issue has been fixed in version 0.10.6.1.
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Analysis
by VulDB Data Team • 07/20/2026
The xrdp vulnerability represents a critical denial of service flaw that exploits improper input validation within the Remote Desktop Protocol implementation. This vulnerability affects versions 0.10.6 and prior, where the software fails to adequately validate the totalLength field in RDP protocol control headers during packet processing. The flaw manifests when an attacker sends maliciously crafted packets that manipulate the protocol data unit structure, specifically targeting the internal pointer advancement mechanism. The vulnerability operates at the core protocol parsing layer where the xrdp service processes incoming RDP connections, creating a condition where the processing loop becomes trapped in an infinite cycle without proper pointer movement. This type of vulnerability falls under CWE-129, Input Validation and Representation, and more specifically aligns with CWE-784, Reliance on Client-Side Controls, as it demonstrates how insufficient server-side validation can lead to resource exhaustion. The issue is particularly dangerous because it requires no authentication to exploit, making it accessible to any remote attacker who can establish network connectivity to the vulnerable service.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise entire system availability. When exploited, the vulnerability forces the xrdp process or thread into a CPU-bound infinite loop where internal pointers fail to advance properly through the packet data structure. The bypassing of deadlock prevention mechanisms for specific protocol data unit types creates a persistent resource consumption scenario that can exhaust available CPU cycles indefinitely. This condition affects not only the targeted xrdp service but can also impact overall system performance by consuming excessive computational resources that should be allocated to legitimate user sessions and system operations. The vulnerability's design allows for multiple concurrent connections to compound the resource exhaustion effect, potentially leading to complete system compromise or denial of service for all users attempting to establish valid RDP connections. From an attacker perspective, this represents a low-effort, high-impact vector that aligns with ATT&CK technique T1499.004 for network denial of service attacks.
The fix implemented in version 0.10.6.1 addresses the root cause by introducing proper validation of the totalLength field within the RDP protocol control header and ensuring that internal pointer advancement occurs correctly regardless of packet content. This remediation follows best practices for protocol implementation security by enforcing strict bounds checking and preventing malformed data from causing unintended execution paths. The solution incorporates defensive programming techniques that prevent the infinite loop condition while maintaining compatibility with legitimate RDP traffic patterns. Organizations should prioritize immediate deployment of this patch across all systems running vulnerable xrdp versions, as the vulnerability provides no authentication requirements for exploitation and can be readily automated through network scanning tools. Additionally, implementing network-level protections such as firewall rules to restrict access to RDP ports from trusted sources can provide additional defense in depth while the patch is being deployed. The vulnerability serves as a reminder of the critical importance of proper input validation in protocol implementations and demonstrates how seemingly minor parsing flaws can result in significant operational impacts when exploited at scale.