CVE-2018-8788 in FreeRDP
Summary
by MITRE
FreeRDP prior to version 2.0.0-rc4 contains an Out-Of-Bounds Write of up to 4 bytes in function nsc_rle_decode() that results in a memory corruption and possibly even a remote code execution.
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Analysis
by VulDB Data Team • 06/12/2023
The vulnerability identified as CVE-2018-8788 represents a critical memory corruption flaw within the FreeRDP remote desktop protocol implementation that affects versions prior to 2.0.0-rc4. This issue manifests as an out-of-bounds write condition in the nsc_rle_decode() function, which is responsible for decoding RLE (Run-Length Encoding) compressed data during remote desktop sessions. The flaw occurs when processing maliciously crafted RLE-encoded data, specifically within the network streams used for graphics rendering in remote desktop connections. The vulnerability stems from inadequate bounds checking during decompression operations, allowing an attacker to write up to four bytes beyond the allocated memory buffer.
The technical implementation of this vulnerability involves the nsc_rle_decode() function failing to properly validate input data lengths and compression parameters before performing memory operations. When FreeRDP processes RLE-encoded graphics data from a remote server, the function attempts to decode compressed pixel information without sufficient boundary validation. This oversight creates a scenario where attacker-controlled data can cause memory writes beyond the intended buffer boundaries, potentially corrupting adjacent memory regions. The specific nature of the out-of-bounds write affects memory corruption patterns that could be exploited to achieve arbitrary code execution. According to CWE-787, this vulnerability maps directly to out-of-bounds write conditions that can lead to memory corruption, while the ATT&CK framework categorizes this under privilege escalation and code execution techniques through memory corruption vulnerabilities.
The operational impact of CVE-2018-8788 extends beyond simple memory corruption, as it presents a significant remote code execution risk for systems running vulnerable FreeRDP implementations. Attackers can leverage this vulnerability by establishing a remote desktop connection to a target system and transmitting specially crafted RLE-encoded graphics data that triggers the memory corruption. The potential for remote code execution makes this vulnerability particularly dangerous in enterprise environments where remote desktop services are commonly deployed. Systems utilizing FreeRDP for remote desktop connections, including those implementing Microsoft Remote Desktop Protocol (RDP) clients, are at risk. The vulnerability affects not only direct RDP connections but also any application or service that relies on FreeRDP for remote desktop functionality, potentially compromising servers, workstations, and network infrastructure components that depend on this remote access technology.
Mitigation strategies for CVE-2018-8788 primarily focus on immediate version upgrades to FreeRDP 2.0.0-rc4 or later, which contain the necessary patches to address the out-of-bounds write condition. Organizations should implement comprehensive patch management procedures to ensure all systems utilizing FreeRDP are updated promptly. Network segmentation and access controls should be enforced to limit exposure of systems running vulnerable FreeRDP implementations. Additional defensive measures include implementing network monitoring to detect unusual RDP traffic patterns and establishing intrusion detection systems that can identify potential exploitation attempts. Security teams should also consider disabling unnecessary RDP services and implementing strong authentication mechanisms to reduce attack surface. The vulnerability highlights the importance of proper input validation and bounds checking in cryptographic and compression libraries, emphasizing the need for rigorous security testing of remote desktop protocol implementations and adherence to secure coding practices that prevent memory corruption vulnerabilities.