CVE-2018-20175 in rdesktop
Summary
by MITRE
rdesktop versions up to and including v1.8.3 contains several Integer Signedness errors that lead to Out-Of-Bounds Reads in the file mcs.c and result in a Denial of Service (segfault).
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Analysis
by VulDB Data Team • 08/01/2023
The vulnerability identified as CVE-2018-20175 affects rdesktop versions up to and including v1.8.3 and represents a critical security flaw stemming from integer signedness errors within the mcs.c file. This issue manifests as out-of-bounds read conditions that ultimately result in denial of service through segmentation faults. The vulnerability resides in the handling of integer values during the processing of Microsoft Remote Desktop Protocol connections, specifically within the Multi-Channel Services component that manages channel establishment and communication.
The technical root cause involves signedness errors in integer variables that are expected to contain unsigned values or sizes. When processing connection parameters or channel data structures, the application fails to properly validate or handle signed integer values that should represent array indices, buffer sizes, or length parameters. This mismanagement leads to scenarios where a maliciously crafted RDP packet can cause the application to attempt reading memory locations beyond the bounds of allocated buffers. The flaw is particularly dangerous because it occurs during the normal connection establishment process, making it exploitable by remote attackers without requiring authentication.
From an operational perspective, this vulnerability creates a significant risk for organizations relying on rdesktop for remote desktop connectivity. The denial of service condition results in segmentation faults that crash the rdesktop client application, effectively preventing legitimate users from establishing remote connections. This can lead to extended downtime for administrators and users who depend on remote access capabilities, particularly in enterprise environments where remote desktop services are critical for business operations. The vulnerability's exploitation requires minimal effort from attackers, as it can be triggered through malformed RDP packets sent to the client application.
The impact of this vulnerability aligns with CWE-195: Signed to Unsigned Conversion Error and CWE-129: Improper Validation of Array Index, both of which are fundamental issues in memory safety and input validation. From an attacker perspective, this vulnerability maps to ATT&CK technique T1203: Exploitation for Client Execution, as it allows for remote code execution through service disruption, though the primary impact is denial of service rather than direct code execution. Organizations should prioritize immediate patching of affected rdesktop installations to prevent exploitation, as the vulnerability can be leveraged by attackers to disrupt remote access services and potentially create opportunities for further attacks against compromised systems.
Mitigation strategies should include immediate deployment of patched rdesktop versions, network segmentation to limit exposure of vulnerable systems, and implementation of intrusion detection systems to monitor for suspicious RDP traffic patterns. Additionally, organizations should consider implementing additional access controls and authentication measures to reduce the attack surface and prevent unauthorized exploitation attempts. The vulnerability highlights the importance of proper integer validation and bounds checking in network protocol implementations, particularly in applications handling untrusted input from remote sources.