CWE-553 Variant Incomplete

Command Shell in Externally Accessible Directory

This vulnerability occurs when a command shell script is placed in a web-accessible directory, such as /cgi-bin/. Attackers can directly request this file to execute arbitrary commands on the…

Definition

What is CWE-553?

This vulnerability occurs when a command shell script is placed in a web-accessible directory, such as /cgi-bin/. Attackers can directly request this file to execute arbitrary commands on the server, leading to full system compromise.
Web servers are designed to serve specific file types, like HTML or images, and to execute authorized scripts in controlled ways. When a shell script (e.g., a .sh or .bat file) is mistakenly uploaded or created in a publicly accessible folder, it bypasses these normal application controls. An attacker can simply trigger the script via a web request, causing the server to run any commands embedded within it with the web server's permissions. To prevent this, enforce strict inventory controls for all files in web directories. Development and deployment processes should never place interpreter shells or administrative scripts within the document root or other accessible locations. Regularly audit these directories for unauthorized files, and configure web server rules to block execution of known script extensions in static content areas.
Real-world impact

Real-world CVEs caused by CWE-553

No public CVE references are linked to this CWE in MITRE's catalog yet.

How attackers exploit it

Step-by-step attacker path

  1. 1

    Identify a code path that handles untrusted input without validation.

  2. 2

    Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.

  3. 3

    Deliver the payload through a normal request and observe the application's reaction.

  4. 4

    Iterate until the response leaks data, executes attacker code, or escalates privileges.

Vulnerable code example

Vulnerable pseudo

MITRE has not published a code example for this CWE. The pattern below is illustrative — see Resources for canonical references.

Vulnerable pseudo 
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
  // Untrusted input flows directly into the sensitive sink.
  return executeUnsafe(input);
}
Secure code example

Secure pseudo

Secure pseudo 
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
  const safe = validateAndEscape(input);
  return executeWithGuards(safe);
}
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist

How to prevent CWE-553

  • Installation / System Configuration Remove any Shells accessible under the web root folder and children directories.
Detection signals

How to detect CWE-553

SAST High

Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.

DAST Moderate

Run dynamic application security testing against the live endpoint.

Runtime Moderate

Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.

Code review Moderate

Code review: flag any new code that handles input from this surface without using the validated framework helpers.

Plexicus auto-fix

Plexicus auto-detects CWE-553 and opens a fix PR in under 60 seconds.

Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.

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Frequently asked questions

Frequently asked questions

What is CWE-553?

This vulnerability occurs when a command shell script is placed in a web-accessible directory, such as /cgi-bin/. Attackers can directly request this file to execute arbitrary commands on the server, leading to full system compromise.

How serious is CWE-553?

MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.

What languages or platforms are affected by CWE-553?

MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.

How can I prevent CWE-553?

Remove any Shells accessible under the web root folder and children directories.

How does Plexicus detect and fix CWE-553?

Plexicus's SAST engine matches the data-flow signature for CWE-553 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-553?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/553.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-553

CWE-552 Parent

Files or Directories Accessible to External Parties

This vulnerability occurs when an application exposes files or directories to users who shouldn't have access to them.

CWE-219 Sibling

Storage of File with Sensitive Data Under Web Root

This vulnerability occurs when an application saves sensitive files, such as configuration data or private keys, inside the web server's…

CWE-220 Sibling

Storage of File With Sensitive Data Under FTP Root

This vulnerability occurs when an application saves sensitive files, such as configuration or user data, within the directory served by an…

CWE-527 Sibling

Exposure of Version-Control Repository to an Unauthorized Control Sphere

This vulnerability occurs when a version control repository, like Git or SVN, is accidentally placed in a location accessible to…

CWE-528 Sibling

Exposure of Core Dump File to an Unauthorized Control Sphere

This vulnerability occurs when an application creates a core dump file (a snapshot of memory at the time of a crash) and places it in a…

CWE-529 Sibling

Exposure of Access Control List Files to an Unauthorized Control Sphere

This vulnerability occurs when an application stores sensitive access control list (ACL) files in a location that is accessible to…

CWE-530 Sibling

Exposure of Backup File to an Unauthorized Control Sphere

This vulnerability occurs when backup or temporary files are stored in locations that unauthorized users can access, such as web…

CWE-539 Sibling

Use of Persistent Cookies Containing Sensitive Information

This vulnerability occurs when a web application stores sensitive data, like authentication details or personal information, within…

Resources

Further reading

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