CWE-48 Variant Incomplete

Path Equivalence: 'file name' (Internal Whitespace)

This vulnerability occurs when an application accepts file paths containing internal spaces (like 'file name') without proper validation. Attackers can exploit this ambiguity to bypass security…

Definition

What is CWE-48?

This vulnerability occurs when an application accepts file paths containing internal spaces (like 'file name') without proper validation. Attackers can exploit this ambiguity to bypass security checks, potentially accessing files or directories outside the intended scope.
File systems and security filters often handle paths with internal spaces inconsistently. An attacker can submit a path like 'important document' when the system expects 'important_document' or 'important%20document'. This mismatch can trick the application's validation logic, allowing the request to proceed to the underlying operating system, which may resolve it to a legitimate but unintended file. To prevent this, developers must normalize and strictly validate all user-supplied path inputs before processing. Implement a canonicalization step that removes or rejects internal whitespace, and use allowlists for permitted directory locations. Never rely solely on blacklisting specific characters or patterns, as file system interpretation can vary across platforms.
Real-world impact

Real-world CVEs caused by CWE-48

  • CVE-2000-0293

    Filenames with spaces allow arbitrary file deletion when the product does not properly quote them; some overlap with path traversal.

  • CVE-2001-1567

    "+" characters in query string converted to spaces before sensitive file/extension (internal space), leading to bypass of access restrictions to the 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-48

  • 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-48

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

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Frequently asked questions

Frequently asked questions

What is CWE-48?

This vulnerability occurs when an application accepts file paths containing internal spaces (like 'file name') without proper validation. Attackers can exploit this ambiguity to bypass security checks, potentially accessing files or directories outside the intended scope.

How serious is CWE-48?

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-48?

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

How can I prevent CWE-48?

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-48?

Plexicus's SAST engine matches the data-flow signature for CWE-48 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-48?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/48.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-48

CWE-41 Parent

Improper Resolution of Path Equivalence

This vulnerability occurs when an application fails to properly handle different text representations that refer to the same file or…

CWE-42 Sibling

Path Equivalence: 'filename.' (Trailing Dot)

This vulnerability occurs when a system accepts file or directory paths that end with a dot (like 'file.txt.' or 'folder.') without…

CWE-44 Sibling

Path Equivalence: 'file.name' (Internal Dot)

This vulnerability occurs when an application accepts file paths containing internal dots (like 'file.ordir') without properly checking…

CWE-46 Sibling

Path Equivalence: 'filename ' (Trailing Space)

This vulnerability occurs when an application processes file paths that end with a space character (like 'document.txt ') without properly…

CWE-47 Sibling

Path Equivalence: ' filename' (Leading Space)

This vulnerability occurs when an application accepts file or directory paths that begin with a space character (like ' filename'),…

CWE-49 Sibling

Path Equivalence: 'filename/' (Trailing Slash)

This vulnerability occurs when an application accepts file or directory paths that end with a slash (e.g., 'documents/') without properly…

CWE-50 Sibling

Path Equivalence: '//multiple/leading/slash'

This vulnerability occurs when an application accepts file or directory paths containing multiple leading slashes (like…

CWE-51 Sibling

Path Equivalence: '/multiple//internal/slash'

This vulnerability occurs when an application accepts file or directory paths containing multiple consecutive forward slashes (e.g.,…

CWE-52 Sibling

Path Equivalence: '/multiple/trailing/slash//'

This vulnerability occurs when an application accepts file or directory paths containing multiple consecutive forward slashes (like…

Resources

Further reading

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