CVE-2016-7543 in Bash
Summary
by MITRE
Bash before 4.4 allows local users to execute arbitrary commands with root privileges via crafted SHELLOPTS and PS4 environment variables.
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Analysis
by VulDB Data Team • 05/14/2026
The vulnerability identified as CVE-2016-7543 represents a critical privilege escalation flaw in the GNU Bourne Again Shell commonly known as bash. This vulnerability affects bash versions prior to 4.4 and enables local attackers to execute arbitrary code with elevated privileges, potentially compromising system integrity and security. The flaw specifically exploits the interaction between two environment variables SHELLOPTS and PS4, which are typically used for shell options and debugging output respectively. When these variables contain maliciously crafted content, they can be leveraged to trigger command execution during shell initialization processes.
The technical mechanism behind this vulnerability stems from bash's handling of environment variables during shell startup. The SHELLOPTS variable controls shell options while PS4 defines the prompt string for debugging output. When bash processes these variables during initialization, it fails to properly sanitize their contents, allowing attackers to inject malicious commands that get executed with the privileges of the user running the shell. This particular vulnerability is classified under CWE-78 as a command injection flaw, where attacker-controlled data is directly incorporated into shell commands without adequate validation or sanitization. The vulnerability is particularly dangerous because it can be exploited even when the shell is running in a privileged context, making it a prime target for attackers seeking to escalate their privileges within a compromised system.
The operational impact of CVE-2016-7543 extends beyond simple privilege escalation to encompass broader system compromise capabilities. Attackers can leverage this vulnerability to execute arbitrary commands with root privileges, potentially leading to complete system takeover. The vulnerability is particularly concerning in environments where bash is used in conjunction with setuid programs or when users have the ability to influence environment variables. This flaw can be exploited in various attack scenarios including web application vulnerabilities, server misconfigurations, or through malicious software that manipulates environment variables. The attack vector aligns with ATT&CK technique T1068 which describes privilege escalation through local exploitation, and specifically targets the execution of malicious code with elevated privileges.
Mitigation strategies for CVE-2016-7543 focus primarily on patching affected bash installations to version 4.4 or later, which includes proper sanitization of environment variables during shell initialization. System administrators should also implement environment variable validation and sanitization practices, particularly in applications that rely on bash for command execution. Additional protective measures include monitoring for suspicious environment variable modifications, implementing proper access controls to prevent unauthorized environment variable manipulation, and conducting regular security audits of shell configurations. Organizations should also consider implementing runtime protections such as stack canaries or address space layout randomization to make exploitation more difficult. The vulnerability serves as a reminder of the critical importance of proper input validation and sanitization in shell environments, particularly when dealing with user-controllable data that may be processed through command execution mechanisms.