CWE-49 Variant Incomplete

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 normalizing them. This can confuse the system's path…

Definition

What is CWE-49?

This vulnerability occurs when an application accepts file or directory paths that end with a slash (e.g., 'documents/') without properly normalizing them. This can confuse the system's path resolution logic, potentially allowing an attacker to bypass security checks and access files or directories they shouldn't.
At its core, this issue is about inconsistent path handling. Many file systems and APIs treat a path like 'public/data' and 'public/data/' as equivalent, pointing to the same directory. However, an application's custom security logic—like an allowlist or a path traversal check—might only validate the first version. When the system later resolves the trailing slash version to its canonical form, it could access a resource that bypassed the initial validation. To prevent this, developers should always normalize paths before performing any security operations. This means stripping trailing slashes (or adding them consistently) and converting the path to a single, standard format. Rely on well-tested library functions for path canonicalization instead of custom string checks, and apply all authorization rules after normalization to ensure the validated path is the same one the operating system ultimately uses.
Real-world impact

Real-world CVEs caused by CWE-49

  • CVE-2002-0253

    Overlaps infoleak

  • CVE-2001-0446

    Application server allows remote attackers to read source code for .jsp files by appending a / to the requested URL.

  • CVE-2004-0334

    Bypass Basic Authentication for files using trailing "/"

  • CVE-2001-0893

    Read sensitive files with trailing "/"

  • CVE-2001-0892

    Web server allows remote attackers to view sensitive files under the document root (such as .htpasswd) via a GET request with a trailing /.

  • CVE-2004-1814

    Directory traversal vulnerability in server allows remote attackers to read protected files via .. (dot dot) sequences in an HTTP request.

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-49

  • 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-49

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-49 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-49?

This vulnerability occurs when an application accepts file or directory paths that end with a slash (e.g., 'documents/') without properly normalizing them. This can confuse the system's path resolution logic, potentially allowing an attacker to bypass security checks and access files or directories they shouldn't.

How serious is CWE-49?

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-49?

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

How can I prevent CWE-49?

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-49?

Plexicus's SAST engine matches the data-flow signature for CWE-49 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-49?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/49.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-49

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-48 Sibling

Path Equivalence: 'file name' (Internal Whitespace)

This vulnerability occurs when an application accepts file paths containing internal spaces (like 'file name') without proper validation.…

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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