CVE-2018-20180 in rdesktop
Summary
by MITRE
rdesktop versions up to and including v1.8.3 contain an Integer Underflow that leads to a Heap-Based Buffer Overflow in the function rdpsnddbg_process() and results in memory corruption and probably even a remote code execution.
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Analysis
by VulDB Data Team • 08/01/2023
The vulnerability identified as CVE-2018-20180 represents a critical security flaw in rdesktop versions up to and including v1.8.3 that demonstrates a classic integer underflow condition leading to heap-based buffer overflow. This vulnerability exists within the rdpsnddbg_process() function, which handles audio debugging operations in the rdesktop remote desktop protocol client implementation. The integer underflow occurs when processing certain malformed audio data packets, specifically during the calculation of buffer sizes for audio samples. When an attacker crafts malicious audio data with specifically calculated values, the underflow condition causes the integer value to wrap around to a very large positive number, which then gets used as a buffer size parameter. This results in the allocation of an undersized buffer that cannot accommodate the actual audio data being processed, creating a heap-based buffer overflow scenario.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially enable remote code execution within the context of the rdesktop process. When the buffer overflow occurs, it can overwrite adjacent memory locations including return addresses, function pointers, or other critical program state information. This memory corruption can be exploited by an attacker who controls the input data to manipulate the program flow and execute arbitrary code on the victim's system. The vulnerability affects systems running rdesktop versions that support the RDP audio debugging functionality, particularly those configured to process audio streams from remote RDP connections. The attack vector requires the victim to establish an RDP connection to a malicious server that can send crafted audio debugging packets, making this a remote exploitation scenario that does not require local system access.
This vulnerability maps to CWE-190, Integer Overflow or Wraparound, and CWE-121, Stack-based Buffer Overflow, while also aligning with ATT&CK technique T1059.007 for Command and Scripting Interpreter and T1068 for Exploitation for Privilege Escalation. The integer underflow condition creates a chain of memory corruption that can be leveraged for privilege escalation attacks, particularly when the rdesktop process runs with elevated privileges. Security researchers have noted that the vulnerability is particularly dangerous because it occurs in a function that processes audio data, which is commonly transmitted over RDP connections, making it a realistic attack surface. The exploitation requires careful crafting of audio data packets and understanding of the target system's memory layout, but once successful, provides attackers with a mechanism to execute arbitrary code on systems running vulnerable rdesktop versions.
Mitigation strategies for CVE-2018-20180 focus primarily on upgrading to patched versions of rdesktop, specifically versions beyond v1.8.3 where the integer underflow has been addressed through proper input validation and boundary checking. System administrators should also implement network segmentation to limit access to RDP services and ensure that only trusted sources can establish RDP connections. Additional defensive measures include disabling audio debugging features when not required, implementing network monitoring to detect anomalous audio packet patterns, and applying the principle of least privilege to rdesktop processes. Organizations should also consider deploying intrusion detection systems that can identify potential exploitation attempts through unusual memory access patterns or buffer overflow indicators. The vulnerability highlights the importance of robust input validation in network protocol implementations and the necessity of thorough testing for integer overflow conditions in security-critical applications.