CVE-2017-15924 in shadowsocks-libev
Summary
by MITRE
In manager.c in ss-manager in shadowsocks-libev 3.1.0, improper parsing allows command injection via shell metacharacters in a JSON configuration request received via 127.0.0.1 UDP traffic, related to the add_server, build_config, and construct_command_line functions.
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Analysis
by VulDB Data Team • 01/05/2023
The vulnerability CVE-2017-15924 represents a critical command injection flaw in the shadowsocks-libev library version 3.1.0, specifically within the ss-manager component responsible for managing shadowsocks server instances. This vulnerability arises from improper input validation and sanitization of JSON configuration requests processed through UDP traffic on the localhost interface. The flaw affects the manager.c file where the add_server, build_config, and construct_command_line functions fail to properly escape or validate shell metacharacters present in user-supplied configuration data. The attack vector leverages the fact that these functions directly incorporate untrusted input into shell command execution contexts without adequate sanitization, creating a pathway for malicious actors to inject arbitrary commands that will be executed by the system shell.
The technical implementation of this vulnerability stems from a lack of proper input validation and shell escaping mechanisms within the configuration parsing logic. When legitimate configuration requests are received via UDP on 127.0.0.1, the ss-manager component processes these JSON payloads through functions that construct shell commands dynamically. The build_config and construct_command_line functions concatenate user-provided parameters directly into command strings without proper sanitization of special shell characters such as semicolons, pipes, backticks, or other metacharacters that could alter command execution flow. This design pattern aligns with CWE-78, which specifically addresses improper neutralization of special elements used in shell commands, making the system susceptible to command injection attacks. The vulnerability is particularly dangerous because it operates within the privileged manager process that typically runs with elevated privileges, potentially allowing attackers to execute arbitrary code with the same permissions as the shadowsocks manager service.
The operational impact of CVE-2017-15924 extends beyond simple command execution, as it provides attackers with a potential foothold for more sophisticated attacks within the network infrastructure. Since the vulnerability is accessible via UDP traffic to localhost, attackers could potentially exploit it through various attack vectors including local privilege escalation, remote code execution, or service disruption. The attack requires minimal network access since it targets the loopback interface, making it particularly stealthy and difficult to detect through standard network monitoring. The vulnerability also maps to ATT&CK technique T1059.001, which covers command and scripting interpreter execution, and T1068, which addresses exploit for privilege escalation. Organizations using shadowsocks-libev versions 3.1.0 are at significant risk as this vulnerability can be exploited by attackers with access to the local network or those who can send UDP packets to the manager interface, potentially leading to complete compromise of the shadowsocks infrastructure and all associated encrypted communications.
Mitigation strategies for CVE-2017-15924 should prioritize immediate patching of the shadowsocks-libev library to version 3.1.1 or later, which contains the necessary fixes for proper input validation and shell escaping. Organizations should also implement network segmentation to restrict access to the UDP ports used by ss-manager, particularly limiting access to localhost or trusted network segments only. Additional defensive measures include implementing strict input validation at the application level, using parameterized command execution instead of string concatenation, and monitoring for suspicious patterns in UDP traffic to the manager interface. The vulnerability highlights the importance of proper secure coding practices, particularly in handling user input within shell command contexts, and serves as a reminder of the critical need for input sanitization and proper privilege separation in network security tools. Organizations should also consider implementing intrusion detection systems to monitor for unusual command execution patterns and establish regular security audits of network infrastructure components to identify similar vulnerabilities in other software packages.