What is Command Injection?

Command injection is a vulnerability that allows attackers to execute arbitrary operating system commands on the server hosting an application through manipulated input.

What is command injection?

Command injection occurs when an application passes unsanitized user input to a system shell for execution. Attackers inject operating system commands by appending shell metacharacters like semicolons, pipes, or backticks to legitimate input. Successful exploitation grants the attacker the ability to execute arbitrary commands with the privileges of the application process.

How does command injection differ from code injection?

Command injection targets the operating system shell to execute system-level commands while code injection targets the application's programming language interpreter. Command injection uses shell metacharacters to chain commands whereas code injection inserts executable code in the application's language such as Python eval or PHP include vulnerabilities.

What are common command injection techniques?

Attackers use shell metacharacters including semicolons, pipes, ampersands, backticks, and dollar-parentheses to inject commands. Blind command injection uses time-based techniques or out-of-band channels when output is not reflected. Attackers may also leverage environment variable manipulation and command substitution to bypass input filters.

How can developers prevent command injection?

The most effective prevention is avoiding system shell calls entirely by using language-native libraries and APIs instead. When shell commands are unavoidable, use parameterized commands or allowlist-based input validation. Never construct shell commands by concatenating user input. Implement least privilege for application service accounts to limit post-exploitation impact.

How does ioSENTRIX test for command injection?

ioSENTRIX testers manually probe all input vectors that may interact with operating system commands, including form fields, HTTP headers, file names, and API parameters. We test for both reflected and blind command injection using time-based payloads and out-of-band techniques. Our manual approach identifies injection points that automated scanners overlook.

What is blind command injection?

Blind command injection occurs when the application is vulnerable but does not return command output in the response. Testers detect it using time-based payloads that cause measurable delays or out-of-band techniques that trigger DNS lookups or HTTP requests to attacker-controlled servers. Blind injection is equally dangerous because attackers can still exfiltrate data and establish persistence.

What is the impact of successful command injection?

Successful command injection typically results in complete server compromise. Attackers can read sensitive files, modify data, install backdoors, pivot to internal networks, and exfiltrate databases. Because commands execute at the OS level with application process privileges, this vulnerability class is consistently rated as critical severity in security assessments.

What is the relationship between command injection and web shells?

Command injection is often the initial exploitation vector that enables web shell deployment. Once an attacker achieves command execution, they can download and install a web shell for persistent interactive access. The web shell then provides a more convenient interface for ongoing exploitation without requiring repeated injection through the original vulnerability.