CWE-558 Variant Draft

Use of getlogin() in Multithreaded Application

Using the getlogin() function in a multithreaded application can lead to unreliable or incorrect username results, creating security and logic flaws.

Definition

What is CWE-558?

Using the getlogin() function in a multithreaded application can lead to unreliable or incorrect username results, creating security and logic flaws.
The getlogin() function retrieves the username associated with the current process, but it is not thread-safe (non-reentrant). In a multithreaded environment, if another thread or process calls getlogin() simultaneously or modifies the underlying data, the string it returns can be overwritten or changed before your code uses it. This race condition means you cannot trust the value it provides, potentially leading to incorrect access decisions, faulty logging, or corrupted user sessions. To avoid this vulnerability, developers should use secure, thread-safe alternatives. On POSIX systems, consider functions like getpwuid(geteuid()) or environment variables verified in a secure manner, ensuring the user identity remains consistent and reliable throughout the application's execution. Always validate that your chosen method is explicitly designed for concurrent execution contexts.
Real-world impact

Real-world CVEs caused by CWE-558

No public CVE references are linked to this CWE in MITRE's catalog yet.

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 C

The following code relies on getlogin() to determine whether or not a user is trusted. It is easily subverted.

Vulnerable C 
pwd = getpwnam(getlogin());
  if (isTrustedGroup(pwd->pw_gid)) {
  	allow();
  } else {
  	deny();
  }
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-558

  • Architecture and Design Using names for security purposes is not advised. Names are easy to forge and can have overlapping user IDs, potentially causing confusion or impersonation.
  • Implementation Use getlogin_r() instead, which is reentrant, meaning that other processes are locked out from changing the username.
Detection signals

How to detect CWE-558

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-558?

Using the getlogin() function in a multithreaded application can lead to unreliable or incorrect username results, creating security and logic flaws.

How serious is CWE-558?

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-558?

MITRE lists the following affected platforms: C, C++.

How can I prevent CWE-558?

Using names for security purposes is not advised. Names are easy to forge and can have overlapping user IDs, potentially causing confusion or impersonation. Use getlogin_r() instead, which is reentrant, meaning that other processes are locked out from changing the username.

How does Plexicus detect and fix CWE-558?

Plexicus's SAST engine matches the data-flow signature for CWE-558 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-558?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/558.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-558

CWE-663 Parent

Use of a Non-reentrant Function in a Concurrent Context

This vulnerability occurs when a program uses a function that is not safe for reentrancy within a concurrent environment, such as…

CWE-479 Sibling

Signal Handler Use of a Non-reentrant Function

This vulnerability occurs when a signal handler in your code calls a function that is not safe to re-enter. If that function is…

Resources

Further reading

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