CWE-65 Variant Incomplete

Windows Hard Link

This vulnerability occurs when a Windows application opens a file or directory without properly verifying if the path points to a hard link. An attacker can exploit this by creating a hard link that…

Definition

What is CWE-65?

This vulnerability occurs when a Windows application opens a file or directory without properly verifying if the path points to a hard link. An attacker can exploit this by creating a hard link that redirects the application to access files outside its intended permissions, potentially leading to unauthorized data manipulation.
Windows hard links allow multiple file paths to point to the same underlying data on disk. If your application doesn't specifically check for and handle these links, an attacker can replace an expected file with a hard link to any other file on the same volume. This bypasses normal path-based security checks, as the application follows the link thinking it's accessing the original file. This becomes dangerous when privileged processes open files without link validation. For example, an attacker could link a temporary log file to a critical system file like AUTOEXEC.BAT. When the high-privilege process writes to what it thinks is a log, it actually overwrites system configuration. Similarly, reading operations could leak sensitive data, and deletion operations could damage system integrity by removing essential files through their alternate links.
Real-world impact

Real-world CVEs caused by CWE-65

  • CVE-2002-0725

    File system allows local attackers to hide file usage activities via a hard link to the target file, which causes the link to be recorded in the audit trail instead of the target file.

  • CVE-2003-0844

    Web server plugin allows local users to overwrite arbitrary files via a symlink attack on predictable temporary filenames.

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-65

  • Architecture and Design Follow the principle of least privilege when assigning access rights to entities in a software system. Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.
Detection signals

How to detect CWE-65

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-65?

This vulnerability occurs when a Windows application opens a file or directory without properly verifying if the path points to a hard link. An attacker can exploit this by creating a hard link that redirects the application to access files outside its intended permissions, potentially leading to unauthorized data manipulation.

How serious is CWE-65?

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-65?

MITRE lists the following affected platforms: Windows.

How can I prevent CWE-65?

Follow the principle of least privilege when assigning access rights to entities in a software system. Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.

How does Plexicus detect and fix CWE-65?

Plexicus's SAST engine matches the data-flow signature for CWE-65 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-65?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/65.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-65

CWE-59 Parent

Improper Link Resolution Before File Access ('Link Following')

This vulnerability occurs when an application uses a filename to access a file but fails to properly check if that name points to a…

CWE-1386 Sibling

Insecure Operation on Windows Junction / Mount Point

This vulnerability occurs when a Windows application opens a file or directory without properly validating that the path is not a symbolic…

CWE-61 Sibling

UNIX Symbolic Link (Symlink) Following

This vulnerability occurs when a software application opens files or directories without properly checking if they are symbolic links…

CWE-62 Sibling

UNIX Hard Link

This vulnerability occurs when an application opens a file or directory without verifying if the name points to a hard link that leads…

CWE-64 Sibling

Windows Shortcut Following (.LNK)

This vulnerability occurs when an application opens a file or directory without properly validating that it is a Windows shortcut (.LNK).…

Resources

Further reading

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