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.)
CWE-243 Variant Draft
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
Identify a code path that handles untrusted input without validation.
- 2
Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.
- 3
Deliver the payload through a normal request and observe the application's reaction.
- 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:
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
// 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
CWE-243
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Frequently asked questions What is CWE-243?
How serious is CWE-243?
What languages or platforms are affected by CWE-243?
How can I prevent CWE-243?
How does Plexicus detect and fix CWE-243?
Where can I learn more about CWE-243?
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.
Related weaknesses
Weaknesses related to CWE-243
CWE-669 Parent
Incorrect Resource Transfer Between Spheres
This vulnerability occurs when an application incorrectly moves or shares a resource (like data, permissions, or functionality) between…
CWE-1420 Sibling
Exposure of Sensitive Information during Transient Execution
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CWE-212 Sibling
Improper Removal of Sensitive Information Before Storage or Transfer
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CWE-434 Sibling
Unrestricted Upload of File with Dangerous Type
This vulnerability occurs when an application accepts file uploads without properly restricting the file types, allowing attackers to…
CWE-494 Sibling
Download of Code Without Integrity Check
This vulnerability occurs when an application fetches and runs code from an external source—like a remote server or CDN—without properly…
CWE-565 Sibling
Reliance on Cookies without Validation and Integrity Checking
This vulnerability occurs when an application uses cookies to make security decisions—like granting access or changing settings—but fails…
CWE-829 Sibling
Inclusion of Functionality from Untrusted Control Sphere
This weakness occurs when an application integrates executable code, like a library or plugin, from a source it does not fully control or…
Resources
Further reading
- MITRE — official CWE-243 https://cwe.mitre.org/data/definitions/243.html
- Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors https://samate.nist.gov/SSATTM_Content/papers/Seven%20Pernicious%20Kingdoms%20-%20Taxonomy%20of%20Sw%20Security%20Errors%20-%20Tsipenyuk%20-%20Chess%20-%20McGraw.pdf
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