CWE-143 Variant Draft

Improper Neutralization of Record Delimiters

This vulnerability occurs when an application fails to properly sanitize or escape special characters that function as record separators in data streams. When untrusted input containing these…

Definition

What is CWE-143?

This vulnerability occurs when an application fails to properly sanitize or escape special characters that function as record separators in data streams. When untrusted input containing these delimiters is passed to a downstream system, it can corrupt data structures, cause misinterpretation of records, or trigger unauthorized actions.
Imagine your application accepts user input—like a form field for a name or address—and later packages that data into a structured format like a CSV file, a log entry, or a protocol message. If an attacker submits input containing a record delimiter (such as a newline, pipe character, or custom separator), and your code doesn't neutralize it, that input can break the expected record boundaries. The downstream parser, whether it's a database, a reporting tool, or another service, will then misinterpret where one record ends and the next begins, leading to data corruption, injection of false records, or logic errors. In practice, this flaw allows data to escape its intended context. For example, a single input field could be parsed as multiple separate records, or critical delimiters could be missing, causing entire records to be merged or skipped. To prevent this, you must always validate and sanitize input by escaping or removing delimiter characters based on the specific data format and context before processing or transmitting the data.
Real-world impact

Real-world CVEs caused by CWE-143

  • CVE-2004-1982

    Carriage returns in subject field allow adding new records to data file.

  • CVE-2001-0527

    Attacker inserts carriage returns and "|" field separator characters to add new user/privileges.

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-143

  • Developers should anticipate that record 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-143

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-143 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-143?

This vulnerability occurs when an application fails to properly sanitize or escape special characters that function as record separators in data streams. When untrusted input containing these delimiters is passed to a downstream system, it can corrupt data structures, cause misinterpretation of records, or trigger unauthorized actions.

How serious is CWE-143?

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-143?

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

How can I prevent CWE-143?

Developers should anticipate that record 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-143?

Plexicus's SAST engine matches the data-flow signature for CWE-143 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-143?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/143.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-143

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-144 Sibling

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)…

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…

Resources

Further reading

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