CWE-62 Variant Incomplete

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 outside its intended security boundary. Attackers can exploit…

Definition

What is CWE-62?

This vulnerability occurs when an application opens a file or directory without verifying if the name points to a hard link that leads outside its intended security boundary. Attackers can exploit this to trick the software into accessing or modifying unauthorized system files.
Hard links allow multiple filenames to reference the same underlying data on a Unix-like filesystem. If a privileged application doesn't validate whether a provided path is a hard link, an attacker can replace an expected file with a link to a critical system file (like /etc/shadow). When the application performs operations, it unknowingly acts on the sensitive target instead. This bypasses intended access controls and can lead to privilege escalation or data corruption. For example, a log rotation tool running with elevated permissions might follow a hard link to overwrite a password file. Developers must explicitly check for hard links when handling files that require strict origin validation, especially in security-sensitive contexts.
Real-world impact

Real-world CVEs caused by CWE-62

  • CVE-2001-1494

    Hard link attack, file overwrite; interesting because program checks against soft links

  • CVE-2002-0793

    Hard link and possibly symbolic link following vulnerabilities in embedded operating system allow local users to overwrite arbitrary files.

  • CVE-2003-0578

    Server creates hard links and unlinks files as root, which allows local users to gain privileges by deleting and overwriting arbitrary files.

  • CVE-1999-0783

    Operating system allows local users to conduct a denial of service by creating a hard link from a device special file to a file on an NFS file system.

  • CVE-2004-1603

    Web hosting manager follows hard links, which allows local users to read or modify arbitrary files.

  • CVE-2004-1901

    Package listing system allows local users to overwrite arbitrary files via a hard link attack on the lockfiles.

  • CVE-2005-0342

    The Finder in Mac OS X and earlier allows local users to overwrite arbitrary files and gain privileges by creating a hard link from the .DS_Store file to an arbitrary file.

  • CVE-2005-1111

    Hard link race condition

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-62

  • 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-62

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-62 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-62?

This vulnerability occurs when an application opens a file or directory without verifying if the name points to a hard link that leads outside its intended security boundary. Attackers can exploit this to trick the software into accessing or modifying unauthorized system files.

How serious is CWE-62?

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-62?

MITRE lists the following affected platforms: Unix.

How can I prevent CWE-62?

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-62?

Plexicus's SAST engine matches the data-flow signature for CWE-62 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-62?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/62.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-62

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-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).…

CWE-65 Sibling

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…

Resources

Further reading

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