CWE-266 Base Draft

Incorrect Privilege Assignment

This vulnerability occurs when a system mistakenly grants a user, process, or entity a specific permission or privilege they should not have. This error creates an unintended level of access,…

Definition

What is CWE-266?

This vulnerability occurs when a system mistakenly grants a user, process, or entity a specific permission or privilege they should not have. This error creates an unintended level of access, allowing the actor to perform actions beyond their intended authority.
Incorrect privilege assignment is a core authorization flaw where the system's security model fails to properly enforce the principle of least privilege. Instead of granting the minimum access necessary for a function, the system erroneously provides elevated rights—such as administrative capabilities, write access to sensitive files, or the ability to modify other users' data. This mistake often stems from misconfigured access control lists (ACLs), flawed role-based access control (RBAC) logic, or errors during user/role provisioning. From a developer's perspective, this vulnerability is frequently introduced during code deployment or user management, rather than within the core application logic itself. Common scenarios include copying permission sets from high-privilege accounts, incorrectly mapping users to roles, or failing to validate inherited permissions. To prevent this, always implement explicit privilege assignment, audit permission changes, and use automated tools to verify that access controls match the intended security policy before deployment.
Real-world impact

Real-world CVEs caused by CWE-266

  • CVE-1999-1193

    untrusted user placed in unix "wheel" group

  • CVE-2005-2741

    Product allows users to grant themselves certain rights that can be used to escalate privileges.

  • CVE-2005-2496

    Product uses group ID of a user instead of the group, causing it to run with different privileges. This is resultant from some other unknown issue.

  • CVE-2004-0274

    Product mistakenly assigns a particular status to an entity, leading to increased privileges.

How attackers exploit it

Step-by-step attacker path

  1. 1

    The following example demonstrates the weakness.

  2. 2

    The following example demonstrates the weakness.

  3. 3

    This application sends a special intent with a flag that allows the receiving application to read a data file for backup purposes.

  4. 4

    Any malicious application can register to receive this intent. Because of the FLAG_GRANT_READ_URI_PERMISSION included with the intent, the malicious receiver code can read the user's data.

Vulnerable code example

Vulnerable C

The following example demonstrates the weakness.

Vulnerable C 
seteuid(0);
```
/* do some stuff */* 
  
  seteuid(getuid());
Attacker payload
Attacker payload Java 
public class CallReceiver extends BroadcastReceiver {
  	@Override
  	public void onReceive(Context context, Intent intent) {
  		Uri userData = intent.getData();
  		stealUserData(userData);
  	}
  }
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-266

  • Architecture and Design / Operation Very carefully manage the setting, management, and handling of privileges. Explicitly manage trust zones in the software.
  • Architecture and Design / Operation Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.
Detection signals

How to detect CWE-266

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-266 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-266?

This vulnerability occurs when a system mistakenly grants a user, process, or entity a specific permission or privilege they should not have. This error creates an unintended level of access, allowing the actor to perform actions beyond their intended authority.

How serious is CWE-266?

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-266?

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

How can I prevent CWE-266?

Very carefully manage the setting, management, and handling of privileges. Explicitly manage trust zones in the software. Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need…

How does Plexicus detect and fix CWE-266?

Plexicus's SAST engine matches the data-flow signature for CWE-266 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-266?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/266.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-266

CWE-269 Parent

Improper Privilege Management

This vulnerability occurs when an application fails to correctly manage user permissions, allowing someone to perform actions or access…

CWE-250 Sibling

Execution with Unnecessary Privileges

This vulnerability occurs when software runs with higher permissions than it actually needs to perform its tasks. This excessive privilege…

CWE-267 Sibling

Privilege Defined With Unsafe Actions

This vulnerability occurs when a system grants a user, role, or process a specific permission that can be misused to perform dangerous,…

CWE-268 Sibling

Privilege Chaining

Privilege chaining occurs when an attacker combines two separate permissions or capabilities, neither of which is dangerous on its own, to…

CWE-270 Sibling

Privilege Context Switching Error

This vulnerability occurs when an application fails to properly manage user permissions while moving between different security contexts,…

CWE-271 Sibling

Privilege Dropping / Lowering Errors

This vulnerability occurs when a system or process fails to reduce its elevated permissions before transferring control of a resource to a…

CWE-274 Sibling

Improper Handling of Insufficient Privileges

This vulnerability occurs when an application fails to properly manage situations where it lacks the necessary permissions to execute an…

CWE-648 Sibling

Incorrect Use of Privileged APIs

This vulnerability occurs when software incorrectly uses functions that require special permissions. Attackers can exploit these mistakes…

CWE-286 Peer

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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