CVE-2026-55238 in xrdp
Summary
by MITRE • 07/20/2026
xrdp is an open source RDP server. Versions 0.10.6 and prior contain a vulnerability concerning the processing of RDP Confirm Active PDU, where during the capability negotiation phase, the parser did not perform sufficient length validation for specific capability sets. A remote, unauthenticated attacker could potentially exploit this flaw by sending a specially crafted RDP packet containing malformed capability data. Due to missing bounds checks, the xrdp process may perform out-of-bounds memory reads, which can result in the termination of the service (Denial of Service). However, since xrdp forks a new process for each connection by default, an out-of-bounds read causing a process crash is unlikely to bring down the entire xrdp service. 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 memory safety issue within the Remote Desktop Protocol implementation that affects versions prior to 0.10.6.1. This flaw exists during the RDP Confirm Active PDU processing phase, specifically during capability negotiation where the server validates incoming connection parameters. The vulnerability stems from inadequate bounds checking mechanisms in the parser responsible for handling capability sets, which are essential components of the RDP protocol used to negotiate supported features and capabilities between client and server. When an attacker crafts malicious RDP packets containing malformed capability data, the vulnerable xrdp server fails to properly validate the length of these structures before processing them.
The technical exploitation of this vulnerability involves sending specially crafted RDP packets that trigger out-of-bounds memory reads within the xrdp process execution flow. This type of flaw falls under the CWE-129 category of "Improper Validation of Array Index" and can be categorized as a buffer over-read condition according to CWE-788. The lack of proper input validation during the capability negotiation phase allows attackers to manipulate memory access patterns that were not anticipated by the original implementation design. This vulnerability directly impacts the integrity of memory management within the xrdp service, potentially leading to undefined behavior and system instability.
From an operational perspective, while this vulnerability does not provide direct execution capabilities or persistence mechanisms, it represents a significant denial of service threat that can disrupt legitimate remote desktop services. The impact is particularly concerning in environments where remote access is critical for business operations, as service disruption can lead to productivity loss and potential security implications during incident response. The fact that xrdp forks new processes for each connection by default provides some mitigation against complete service termination, but individual connections can still be disrupted. This vulnerability affects the availability aspect of the CIA triad and aligns with attack patterns documented in the MITRE ATT&CK framework under the T1499 category of "Endpoint Denial of Service" and potentially T1566 for initial access through network services.
The mitigation strategy involves upgrading to xrdp version 0.10.6.1 or later, which includes proper bounds checking mechanisms for capability set processing. Organizations should also implement network-level protections such as firewall rules that limit RDP access to trusted networks and consider monitoring for unusual RDP traffic patterns that might indicate exploitation attempts. Additionally, regular security assessments of remote access services and maintaining updated security patches across all systems is essential for preventing similar vulnerabilities from being exploited in the broader attack surface. The fix implemented in version 0.10.6.1 demonstrates proper input validation techniques that should be adopted as defensive programming practices throughout similar network service implementations to prevent similar memory safety issues.