CWE-842 Base Incomplete

Placement of User into Incorrect Group

This vulnerability occurs when a system or administrator assigns a user to the wrong security group or role.

Definition

What is CWE-842?

This vulnerability occurs when a system or administrator assigns a user to the wrong security group or role.
When a user is placed into a group with higher privileges than intended, they can bypass security controls. This allows unauthorized access to sensitive data, functions, or system resources that should be off-limits, effectively creating a privilege escalation path. Access control systems typically trust group assignments, so they won't flag this incorrect membership as malicious activity. This makes the issue hard to detect, allowing potential abuse to go unnoticed unless specific user actions are audited against their intended permissions.
Real-world impact

Real-world CVEs caused by CWE-842

  • CVE-1999-1193

    Operating system assigns user to privileged wheel group, allowing the user to gain root privileges.

  • CVE-2010-3716

    Chain: drafted web request allows the creation of users with arbitrary group membership.

  • CVE-2008-5397

    Chain: improper processing of configuration options causes users to contain unintended group memberships.

  • CVE-2007-6644

    CMS does not prevent remote administrators from promoting other users to the administrator group, in violation of the intended security model.

  • CVE-2007-3260

    Product assigns members to the root group, allowing escalation of privileges.

  • CVE-2002-0080

    Chain: daemon does not properly clear groups before dropping privileges.

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-842

  • 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-842

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-842?

This vulnerability occurs when a system or administrator assigns a user to the wrong security group or role.

How serious is CWE-842?

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-842?

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

How can I prevent CWE-842?

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-842?

Plexicus's SAST engine matches the data-flow signature for CWE-842 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-842?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/842.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-842

CWE-286 Parent

Incorrect User Management

This vulnerability occurs when an application incorrectly handles user accounts, roles, or group memberships, leading to improper access…

Resources

Further reading

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