CVE-2017-18266 in Xdg-utils
Summary
by MITRE
The open_envvar function in xdg-open in xdg-utils before 1.1.3 does not validate strings before launching the program specified by the BROWSER environment variable, which might allow remote attackers to conduct argument-injection attacks via a crafted URL, as demonstrated by %s in this environment variable.
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Analysis
by VulDB Data Team • 03/11/2023
The vulnerability CVE-2017-18266 resides in the xdg-open utility within xdg-utils package, specifically affecting versions prior to 1.1.3. This flaw exists in the open_envvar function which processes environment variables to determine which browser to launch for opening URLs. The issue manifests when the BROWSER environment variable contains format specifiers such as %s, which are not properly sanitized before being passed to the system command execution. This represents a classic command injection vulnerability where attacker-controlled input can be interpreted as command arguments rather than simple string data.
The technical implementation of this vulnerability stems from improper input validation within the xdg-open utility's environment variable handling mechanism. When a user or application sets the BROWSER environment variable to include format specifiers like %s, the open_envvar function fails to sanitize these inputs before executing system calls. This allows attackers to inject malicious arguments that can be interpreted by the underlying command execution mechanism. The vulnerability is particularly dangerous because it leverages environment variable manipulation, which is often overlooked in security assessments and can be easily exploited in various attack scenarios.
The operational impact of this vulnerability extends beyond simple argument injection to potentially enable remote code execution in certain contexts. An attacker who can control or influence the BROWSER environment variable can craft malicious URLs that, when processed by xdg-open, could execute unintended commands on the target system. This vulnerability affects desktop environments that rely on xdg-utils for handling URL opening operations, particularly in Linux and Unix-like systems where the Desktop Entry Specification is commonly implemented. The attack vector typically involves web applications or services that trigger xdg-open with user-controllable URL data, making it a significant concern for web-based attack scenarios.
This vulnerability maps directly to CWE-78 and CWE-88 within the CWE database, representing a command injection flaw and argument injection respectively. The ATT&CK framework categorizes this under T1059.007 for command and scripting interpreter with the specific technique of using environment variables for command execution. The attack surface is broad since many applications and services may invoke xdg-open without proper input sanitization, and environment variables are frequently used for configuration purposes. Organizations should note that this vulnerability demonstrates the importance of input validation in system utilities and highlights the risks associated with improper handling of environment variables in command execution contexts. The recommended mitigation involves upgrading to xdg-utils version 1.1.3 or later, where proper input validation has been implemented to prevent format string exploitation. Additionally, system administrators should review and sanitize environment variable configurations, particularly those that influence command execution paths, to reduce the attack surface and prevent potential exploitation.