Shell Shock (Part I)

Shell Shock, more formally known as CVE-2014-6271, CVE-2014-6277, CVE-2014-6278, CVE-2014-7169, CVE-2014-7186, CVE-2014-7187, and CVE-2014-0160, refers to a family of security vulnerabilities discovered in Bash, a widely used command-line shell interpreter. The initial vulnerability, CVE-2014-6271, allows attackers to execute arbitrary commands on vulnerable systems by exploiting the way Bash handles specially crafted environment variables containing function definitions.

Specifically, the vulnerability arises because Bash, when importing a function definition from an environment variable, continues to process commands following the function definition. This allows an attacker to inject malicious commands that will be executed when the Bash shell is invoked.

The potential impact of Shell Shock was significant due to the widespread use of Bash in various operating systems, including Linux and macOS, as well as its presence in numerous embedded systems, web servers (through CGI scripts), and network devices. An attacker could potentially gain unauthorized access to affected systems, execute malicious code, and compromise sensitive data.

Subsequent vulnerabilities (CVE-2014-6277, CVE-2014-6278, CVE-2014-7169, CVE-2014-7186, CVE-2014-7187, and CVE-2014-0160) were discovered after the initial disclosure, representing incomplete fixes or newly discovered attack vectors related to the original issue. These vulnerabilities further complicated mitigation efforts.

The discovery of Shell Shock prompted a widespread effort to patch vulnerable systems. Software vendors released updated versions of Bash to address the flaws, and system administrators were urged to apply these patches as quickly as possible. The remediation process was complex due to the varying levels of Bash implementations across different systems and the need to test patches to ensure compatibility.