CVE-2018-8794 in rdesktop
Summary
by MITRE
rdesktop versions up to and including v1.8.3 contain an Integer Overflow that leads to an Out-Of-Bounds Write in function process_bitmap_updates() and results in a memory corruption and possibly even a remote code execution.
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Analysis
by VulDB Data Team • 07/06/2023
The vulnerability identified as CVE-2018-8794 represents a critical security flaw in rdesktop versions up to and including v1.8.3 that stems from an integer overflow condition within the process_bitmap_updates() function. This issue falls under the broader category of memory safety vulnerabilities and specifically manifests as an out-of-bounds write operation that can lead to arbitrary code execution. The integer overflow occurs when the application processes bitmap update data received from a remote server, where insufficient input validation allows maliciously crafted data to cause unexpected behavior in memory allocation and handling. This vulnerability is particularly dangerous because it can be exploited remotely without requiring authentication, making it a significant threat to systems that rely on rdesktop for remote desktop connections.
The technical implementation of this flaw involves the process_bitmap_updates() function which handles bitmap data received during remote desktop protocol communication. When processing bitmap updates, the application fails to properly validate integer values that determine the size of memory allocations or array bounds. This allows an attacker to manipulate the input data in such a way that the integer overflow results in a memory allocation that is smaller than required, followed by a subsequent write operation that extends beyond the allocated memory boundaries. The vulnerability is classified as a CWE-190 integer overflow, which is a well-documented weakness in software development where arithmetic operations produce values that exceed the maximum representable value for the data type. The specific conditions that trigger this vulnerability involve the manipulation of bitmap header fields that specify dimensions and data sizes, where the overflow creates a scenario where the application writes data beyond the intended memory allocation.
The operational impact of CVE-2018-8794 extends beyond simple memory corruption to potentially enable full remote code execution on affected systems. When an out-of-bounds write occurs in a memory region that is subsequently executed as code, attackers can leverage this condition to inject and run malicious code on the target system. This vulnerability affects systems that utilize rdesktop for remote desktop connections, particularly in enterprise environments where remote access is common. The attack vector requires only a remote connection to a vulnerable rdesktop client, making it particularly dangerous in environments where remote desktop services are exposed to untrusted networks. The vulnerability's potential for remote code execution aligns with ATT&CK technique T1059.007 for command and scripting interpreter, where attackers can execute arbitrary code through manipulated remote desktop connections. Organizations using rdesktop for remote access are particularly at risk, as this vulnerability can be exploited by attackers who gain access to the network segment where the vulnerable client operates.
Mitigation strategies for CVE-2018-8794 primarily focus on immediate remediation through software updates and configuration changes. The most effective immediate solution is to upgrade to rdesktop version 1.8.4 or later, which contains patches specifically designed to address the integer overflow condition in process_bitmap_updates(). System administrators should prioritize patching all affected systems, particularly those that are exposed to external networks or operate in high-risk environments. Additionally, network segmentation and access controls should be implemented to limit exposure of rdesktop clients to untrusted networks. The implementation of input validation controls and bounds checking within the application code can serve as additional defensive measures, though these are less effective than proper software updates. Organizations should also consider implementing network monitoring to detect unusual bitmap update patterns that might indicate exploitation attempts, as this vulnerability can be used in conjunction with other attack vectors to establish persistent access to compromised systems. Security teams should conduct thorough vulnerability assessments to identify all instances of affected rdesktop installations within their network infrastructure and ensure that proper security controls are in place to prevent exploitation of this and similar memory safety vulnerabilities.