CWE-243 Variant Draft High likelihood

Creation of chroot Jail Without Changing Working Directory

This vulnerability occurs when a program creates a chroot jail but fails to change its current working directory afterward. Because the process's working directory remains outside the jail,…

Definition

What is CWE-243?

This vulnerability occurs when a program creates a chroot jail but fails to change its current working directory afterward. Because the process's working directory remains outside the jail, attackers can use relative paths to access files and directories that should be restricted.
The chroot() system call isolates a process within a specific directory subtree, known as a jail. However, a critical step is often missed: chroot() does not automatically change the process's current working directory. If the working directory remains outside the new root, any relative path operations (like opening '../etc/passwd') can still traverse the original filesystem, completely bypassing the intended isolation. To properly secure the jail, you must immediately call chdir('/') after chroot(). This changes the working directory to be inside the new root, ensuring all subsequent relative path references are confined. Without this step, the chroot jail provides a false sense of security and is trivial for an attacker to escape.
Real-world impact

Real-world CVEs caused by CWE-243

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 C

Consider the following source code from a (hypothetical) FTP server:

Vulnerable C 
chroot("/var/ftproot");
  ...
  fgets(filename, sizeof(filename), network);
  localfile = fopen(filename, "r");
  while ((len = fread(buf, 1, sizeof(buf), localfile)) != EOF) {
  	fwrite(buf, 1, sizeof(buf), network);
  }
  fclose(localfile);
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-243

  • Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
  • Implementation Validate input at trust boundaries; use allowlists, not denylists.
  • Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
  • Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
  • Operation Monitor logs for the runtime signals listed in the next section.
Detection signals

How to detect CWE-243

Automated Static Analysis High

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Plexicus auto-fix

Plexicus auto-detects CWE-243 and opens a fix PR in under 60 seconds.

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Frequently asked questions

Frequently asked questions

What is CWE-243?

This vulnerability occurs when a program creates a chroot jail but fails to change its current working directory afterward. Because the process's working directory remains outside the jail, attackers can use relative paths to access files and directories that should be restricted.

How serious is CWE-243?

MITRE rates the likelihood of exploit as High — this weakness is actively exploited in the wild and should be prioritized for remediation.

What languages or platforms are affected by CWE-243?

MITRE lists the following affected platforms: C, C++, Unix.

How can I prevent CWE-243?

Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.

How does Plexicus detect and fix CWE-243?

Plexicus's SAST engine matches the data-flow signature for CWE-243 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-243?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/243.html. You can also reference OWASP and NIST documentation for adjacent guidance.

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Resources

Further reading

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