CVE-2018-20174 in rdesktop
Summary
by MITRE
rdesktop versions up to and including v1.8.3 contain an Out-Of-Bounds Read in the function ui_clip_handle_data() that results in an information leak.
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Analysis
by VulDB Data Team • 08/01/2023
The vulnerability identified as CVE-2018-20174 represents a critical out-of-bounds read flaw within rdesktop versions up to and including v1.8.3. This issue manifests specifically within the ui_clip_handle_data() function, where improper bounds checking allows an attacker to read memory locations beyond the intended buffer boundaries. The vulnerability arises from insufficient validation of input data during clipboard handling operations, creating a scenario where maliciously crafted clipboard data can trigger unauthorized memory access patterns. Such flaws are particularly concerning in remote desktop protocols where clipboard functionality is frequently utilized for data transfer between client and server environments.
The technical implementation of this vulnerability stems from inadequate parameter validation within the clipboard data processing pipeline. When rdesktop processes clipboard data through the ui_clip_handle_data() function, it fails to properly verify the size or content of incoming data structures before attempting to access memory regions. This allows an attacker to craft specially formatted clipboard data that causes the application to read beyond allocated buffer limits, potentially exposing sensitive information from adjacent memory locations. The flaw operates at the application layer and specifically targets the client-side clipboard handling mechanism, making it exploitable during normal remote desktop session operations.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can potentially expose sensitive data such as cryptographic keys, session tokens, or other confidential information stored in adjacent memory regions. An attacker who successfully exploits this vulnerability could gain insights into the internal state of the rdesktop application, potentially leading to more sophisticated attacks including privilege escalation or further exploitation of related vulnerabilities. The information leak aspect of this flaw makes it particularly dangerous in environments where remote desktop services are used for accessing sensitive systems or data repositories. This vulnerability directly aligns with CWE-125, which describes out-of-bounds read conditions, and can be categorized under ATT&CK technique T1059 for execution of malicious code through compromised remote desktop services.
Mitigation strategies for CVE-2018-20174 primarily involve upgrading to rdesktop version 1.8.4 or later, where the bounds checking has been properly implemented to prevent out-of-bounds memory access. Organizations should also implement network segmentation and access controls to limit exposure of remote desktop services to trusted networks only. Additional defensive measures include monitoring clipboard activity for unusual patterns and implementing network-based intrusion detection systems that can identify malformed clipboard data packets. Security teams should also consider disabling clipboard functionality entirely in environments where it is not strictly required, as this removes the attack surface entirely. The fix implemented in the patched versions demonstrates proper input validation techniques that should be adopted as best practices for similar vulnerabilities in other applications handling user-provided data through memory-intensive operations.