CVE-2018-20178 in rdesktop
Summary
by MITRE
rdesktop versions up to and including v1.8.3 contain an Out-Of-Bounds Read in the function process_demand_active() that results in a Denial of Service (segfault).
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Analysis
by VulDB Data Team • 08/01/2023
The vulnerability identified as CVE-2018-20178 represents a critical out-of-bounds read condition within the rdesktop remote desktop protocol client software. This issue affects all versions up to and including v1.8.3, making it a significant concern for organizations relying on remote desktop connectivity. The flaw manifests specifically within the process_demand_active() function, which is responsible for handling demand active messages during the RDP connection establishment phase. When a maliciously crafted RDP server responds to a connection attempt with malformed demand active messages, the rdesktop client fails to properly validate input data before accessing memory regions, leading to a segmentation fault that terminates the application.
The technical implementation of this vulnerability stems from inadequate bounds checking within the RDP protocol processing logic. During the initial negotiation phase of RDP connections, the client receives various demand active messages containing configuration parameters and capabilities. The process_demand_active() function fails to validate the length and structure of incoming data before attempting to read from memory locations that may not be properly allocated or accessible. This type of flaw falls under CWE-129, which specifically addresses insufficient validation of length of input buffers, and can be categorized as a memory safety issue that enables unauthorized code execution or system instability. The vulnerability aligns with ATT&CK technique T1210, which covers exploitation of remote services through malformed input handling, and represents a classic example of how protocol parsing errors can lead to denial of service conditions.
The operational impact of CVE-2018-20178 extends beyond simple service disruption to potentially compromise the availability of critical remote access infrastructure. When exploited, this vulnerability causes the rdesktop client to crash with a segmentation fault, effectively denying legitimate users access to remote desktop services. Organizations that depend on rdesktop for administrative access or remote support operations face significant operational risks, as the vulnerability can be triggered remotely without requiring authentication. The denial of service condition may be particularly problematic in enterprise environments where administrators rely on consistent access to remote systems for maintenance and troubleshooting activities. Additionally, the vulnerability could be leveraged as part of a broader attack chain where attackers first establish a denial of service condition before attempting other exploitation techniques, making it a valuable reconnaissance tool for threat actors.
Mitigation strategies for CVE-2018-20178 should prioritize immediate software updates to versions that have addressed this specific out-of-bounds read condition. The rdesktop development team has released patches in subsequent versions that implement proper bounds checking and input validation within the process_demand_active() function. Organizations should also consider implementing network segmentation and access controls to limit exposure to potentially malicious RDP servers, particularly in environments where untrusted RDP connections are permitted. Additional defensive measures include deploying network monitoring solutions that can detect anomalous RDP traffic patterns and implementing application whitelisting policies to restrict execution of untrusted rdesktop instances. Security teams should also conduct regular vulnerability assessments to identify any remaining instances of affected rdesktop versions within their infrastructure and ensure proper patch management procedures are in place to prevent similar vulnerabilities from occurring in other components of their remote access ecosystem.