Overly Restrictive Account Lockout Mechanism
Weakness ID: 645 (Weakness Base)Status: Incomplete
+ Description

Description Summary

The software contains an account lockout protection mechanism, but the mechanism is too restrictive and can be triggered too easily. This allows attackers to deny service to legitimate users by causing their accounts to be locked out.

Extended Description

Account lockout is a security feature often present in applications as a countermeasure to the brute force attack on the password based authentication mechanism of the system. After a certain number of failed login attempts, the users' account may be disabled for a certain period of time or until it is unlocked by an administrator. Other security events may also possibly trigger account lockout. However, an attacker may use this very security feature to deny service to legitimate system users. It is therefore important to ensure that the account lockout security mechanism is not overly restrictive.

+ Time of Introduction
  • Architecture and Design
+ Applicable Platforms



+ Common Consequences

Users could be locked out of accounts.

+ Likelihood of Exploit


+ Enabling Factors for Exploitation

The system has an account lockout mechanism.

An attacker must be able to trigger the account lockout mechanism.

The cost to the attacker of triggering the account lockout mechanism should be less than the cost to re-enable the account.

+ Observed Examples
A famous example of this type an attack is the eBay attack. eBay always displays the user id of the highest bidder. In the final minutes of the auction, one of the bidders could try to log in as the highest bidder three times. After three incorrect log in attempts, eBay password throttling would kick in and lock out the highest bidder's account for some time. An attacker could then make their own bid and their victim would not have a chance to place the counter bid because they would be locked out. Thus an attacker could win the auction.
+ Potential Mitigations

Implement more intelligent password throttling mechanisms such as those which take IP address into account, in addition to the login name.

Implement a lockout timeout that grows as the number of incorrect login attempts goes up, eventually resulting in a complete lockout.

Consider alternatives to account lockout that would still be effective against password brute force attacks, such as presenting the user machine with a puzzle to solve (makes it do some computation).

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class287Improper Authentication
Development Concepts (primary)699
Research Concepts (primary)1000
+ Content History
Submission DateSubmitterOrganizationSource
2008-01-30Evgeny LebanidzeCigitalExternal Submission
Modification DateModifierOrganizationSource
2008-09-08CWE Content TeamMITREInternal
updated Common Consequences, Enabling Factors for Exploitation, Relationships
2008-10-14CWE Content TeamMITREInternal
updated Description