CVE-2014-6271 in Bash
Summary
by MITRE
GNU Bash through 4.3 processes trailing strings after function definitions in the values of environment variables, which allows remote attackers to execute arbitrary code via a crafted environment, as demonstrated by vectors involving the ForceCommand feature in OpenSSH sshd, the mod_cgi and mod_cgid modules in the Apache HTTP Server, scripts executed by unspecified DHCP clients, and other situations in which setting the environment occurs across a privilege boundary from Bash execution, aka "ShellShock." NOTE: the original fix for this issue was incorrect; CVE-2014-7169 has been assigned to cover the vulnerability that is still present after the incorrect fix.
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Analysis
by VulDB Data Team • 04/22/2026
The vulnerability identified as CVE-2014-6271 represents a critical security flaw in GNU Bash that fundamentally compromised the integrity of Unix-like systems worldwide. This vulnerability, commonly known as "ShellShock," emerged from a fundamental design flaw in how Bash handled environment variables containing function definitions. The flaw occurred when Bash processed environment variables that contained trailing strings after function definitions, creating a dangerous execution path that allowed attackers to inject malicious code into the shell environment. The vulnerability was particularly insidious because it could be exploited across multiple attack vectors and system components, making it one of the most widespread security issues of its time.
The technical implementation of this vulnerability stems from Bash's improper parsing of environment variables during initialization. When Bash encountered environment variables containing function definitions, it would not properly terminate the parsing process at the function definition boundary. Instead, it would continue processing any trailing content as executable commands, creating an arbitrary code execution opportunity. This flaw was categorized under CWE-78 as a command injection vulnerability, where attacker-controlled input was directly executed as shell commands. The vulnerability was particularly dangerous because it could be triggered through various legitimate system interfaces including SSH, web servers, DHCP clients, and other applications that set environment variables across privilege boundaries.
The operational impact of CVE-2014-6271 was catastrophic across the computing landscape, affecting virtually all Unix-like systems that relied on Bash for shell operations. Attackers could exploit this vulnerability to execute arbitrary commands with the privileges of the affected process, potentially leading to complete system compromise. The attack surface was extraordinarily broad, encompassing OpenSSH's ForceCommand feature where remote attackers could inject commands through SSH connections, Apache HTTP Server modules like mod_cgi and mod_cgid that executed scripts with compromised environment variables, and DHCP clients that might receive malicious environment settings. This vulnerability effectively bypassed traditional security controls and could be exploited remotely without authentication, making it particularly dangerous for network services and internet-facing applications.
The remediation efforts for this vulnerability initially proved inadequate, as the first patch released was found to be incomplete and ineffective, leading to the assignment of CVE-2014-7169 to address the remaining vulnerability. Organizations had to implement multiple layers of mitigation including immediate patching of Bash installations, environment variable sanitization, network-level filtering, and monitoring for exploitation attempts. The vulnerability highlighted critical gaps in software security practices and demonstrated the importance of thorough testing of security patches. System administrators were forced to conduct comprehensive audits of their environments, verify patch installations across all affected systems, and implement additional security controls to prevent exploitation. The incident underscored the need for better security practices in software development and the importance of robust vulnerability management processes. This vulnerability ultimately led to significant improvements in how security patches are tested and deployed across enterprise environments, establishing new standards for vulnerability response and remediation procedures that continue to influence security practices today.