CWE-144 Variant Draft

Improper Neutralization of Line Delimiters

This vulnerability occurs when an application fails to properly sanitize or escape line break characters (like newline or carriage return) in user-supplied input before passing that data to another…

Definition

What is CWE-144?

This vulnerability occurs when an application fails to properly sanitize or escape line break characters (like newline or carriage return) in user-supplied input before passing that data to another system or component.
Line delimiters, such as \n or \r\n, are special characters that structure data by marking the end of a line. When an attacker can inject these characters into input fields, they can manipulate how downstream systems—like log parsers, configuration files, or data processors—interpret the data stream. This can trick the receiving component into processing malicious content as separate commands or records, leading to data corruption, security bypasses, or unintended system behavior. In practice, this flaw often manifests when an application blindly trusts input without validation. For example, an attacker might inject a newline into a form field that gets written to a log file, later causing a log analysis tool to misinterpret entries. To prevent this, developers must treat all line-breaking characters as control elements, not data, and implement strict input validation and output encoding specific to the context where the data will be used.
Real-world impact

Real-world CVEs caused by CWE-144

  • CVE-2002-0267

    Linebreak in field of PHP script allows admin privileges when written to data file.

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-144

  • Developers should anticipate that line delimiters will be injected/removed/manipulated in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system.
  • Implementation Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
  • Implementation While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict allowlist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88).
  • Implementation Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Detection signals

How to detect CWE-144

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-144 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-144?

This vulnerability occurs when an application fails to properly sanitize or escape line break characters (like newline or carriage return) in user-supplied input before passing that data to another system or component.

How serious is CWE-144?

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-144?

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

How can I prevent CWE-144?

Developers should anticipate that line delimiters will be injected/removed/manipulated in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system. Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications,…

How does Plexicus detect and fix CWE-144?

Plexicus's SAST engine matches the data-flow signature for CWE-144 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-144?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/144.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-144

CWE-140 Parent

Improper Neutralization of Delimiters

This vulnerability occurs when an application fails to properly handle or sanitize delimiter characters within data inputs, allowing them…

CWE-141 Sibling

Improper Neutralization of Parameter/Argument Delimiters

This vulnerability occurs when an application fails to properly sanitize special characters that act as delimiters in data being passed…

CWE-142 Sibling

Improper Neutralization of Value Delimiters

This vulnerability occurs when an application fails to properly sanitize or escape special characters that act as data separators…

CWE-143 Sibling

Improper Neutralization of Record Delimiters

This vulnerability occurs when an application fails to properly sanitize or escape special characters that function as record separators…

CWE-145 Sibling

Improper Neutralization of Section Delimiters

This vulnerability occurs when an application fails to properly sanitize or validate special characters that act as section delimiters in…

CWE-146 Sibling

Improper Neutralization of Expression/Command Delimiters

This vulnerability occurs when an application fails to properly sanitize input that contains special characters used as delimiters in…

CWE-93 Peer

Improper Neutralization of CRLF Sequences ('CRLF Injection')

This vulnerability occurs when an application uses carriage return and line feed characters (CRLF) to structure data, like separating…

Resources

Further reading

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