CVE-2017-3158 in Terminal Emulator
Summary
by MITRE
A race condition in Guacamole's terminal emulator in versions 0.9.5 through 0.9.10-incubating could allow writes of blocks of printed data to overlap. Such overlapping writes could cause packet data to be misread as the packet length, resulting in the remaining data being written beyond the end of a statically-allocated buffer.
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Analysis
by VulDB Data Team • 12/24/2019
The vulnerability CVE-2017-3158 represents a critical race condition flaw within Apache Guacamole's terminal emulator component that affects versions ranging from 0.9.5 through 0.9.10-incubating. This issue resides in the terminal emulation layer that handles data transmission between remote desktop sessions and client applications. The race condition manifests when multiple threads attempt to write data blocks simultaneously to the terminal buffer, creating a scenario where overlapping write operations can occur. The flaw specifically impacts the packet handling mechanism where printed data blocks may overwrite adjacent memory regions, fundamentally compromising the integrity of the data flow.
The technical implementation of this vulnerability stems from improper synchronization mechanisms within the terminal emulator's buffer management system. When concurrent write operations occur, the system fails to properly coordinate access to the statically-allocated buffer space, allowing one write operation to overwrite data from another. This condition is classified as a buffer overflow vulnerability according to CWE-121, which specifically addresses stack-based buffer overflow conditions. The overlapping writes create a scenario where packet data becomes corrupted, with the actual packet length information being misinterpreted due to the overwritten data. The buffer in question is allocated with fixed size constraints, making it particularly susceptible to this type of memory corruption attack.
The operational impact of CVE-2017-3158 extends beyond simple data corruption, creating potential for more severe security consequences within the Guacamole environment. Attackers could exploit this vulnerability to cause arbitrary code execution or system instability by manipulating the packet data structure. The vulnerability aligns with ATT&CK technique T1059.007, which covers the use of terminal emulation for command execution, and T1068, which addresses local privilege escalation through software vulnerabilities. The overlapping memory writes could potentially be leveraged to overwrite critical control structures within the terminal emulator, enabling attackers to redirect execution flow or inject malicious code into the running process.
Mitigation strategies for this vulnerability require immediate implementation of proper synchronization mechanisms within the terminal emulator codebase. The recommended approach involves implementing mutex locks or similar thread synchronization primitives to ensure that only one write operation can access the buffer at any given time. Additionally, input validation should be strengthened to prevent malformed packet data from causing buffer overflows, as outlined in CWE-122 which addresses heap-based buffer overflow conditions. System administrators should upgrade to Guacamole versions 0.9.11 or later where this race condition has been properly addressed through improved thread management and buffer handling. Network segmentation and monitoring of terminal emulator traffic should also be implemented to detect potential exploitation attempts, aligning with ATT&CK technique T1041 which covers data compression and encryption for exfiltration purposes. The vulnerability demonstrates the importance of proper concurrent programming practices and highlights the need for thorough testing of multi-threaded applications in security-critical systems.