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Weak Password Recovery Mechanism for Forgotten Password

ID: 640Date: (C)2012-05-14   (M)2019-06-02
Type: weaknessStatus: INCOMPLETE
Abstraction Type: Base


The software contains a mechanism for users to recover or change their passwords without knowing the original password, but the mechanism is weak.

Extended Description

It is common for an application to have a mechanism that provides a means for a user to gain access to their account in the event they forget their password. Very often the password recovery mechanism is weak, which has the effect of making it more likely that it would be possible for a person other than the legitimate system user to gain access to that user's account.

This weakness may be that the security question is too easy to guess or find an answer to (e.g. because it is too common). Or there might be an implementation weakness in the password recovery mechanism code that may for instance trick the system into e-mailing the new password to an e-mail account other than that of the user. There might be no throttling done on the rate of password resets so that a legitimate user can be denied service by an attacker if an attacker tries to recover their password in a rapid succession. The system may send the original password to the user rather than generating a new temporary password. In summary, password recovery functionality, if not carefully designed and implemented can often become the system's weakest link that can be misused in a way that would allow an attacker to gain unauthorized access to the system. Weak password recovery schemes completely undermine a strong password authentication scheme.

Enabling Factors for Exploitation
The system allows users to recover their passwords and gain access back into the system.
Password recovery mechanism relies only on something the user knows and not something the user has.
Weak security questions are used.
No third party intervention is required to use the password recovery mechanism.

Likelihood of Exploit: High

Applicable Platforms
Language Class: All

Time Of Introduction

  • Architecture and Design
  • Implementation

Related Attack Patterns

Common Consequences

ScopeTechnical ImpactNotes
Gain privileges / assume identity
An attacker could gain unauthorized access to the system by retrieving legitimate user's authentication credentials.
DoS: resource consumption (other)
An attacker could deny service to legitimate system users by launching a brute force attack on the password recovery mechanism using user ids of legitimate users.
The system's security functionality is turned against the system by the attacker.

Detection Methods

Potential Mitigations

Architecture and Design
 Make sure that all input supplied by the user to the password recovery mechanism is thoroughly filtered and validated.
Architecture and Design
 Do not use standard weak security questions and use several security questions.
Architecture and Design
 Make sure that there is throttling on the number of incorrect answers to a security question. Disable the password recovery functionality after a certain (small) number of incorrect guesses.
Architecture and Design
 Require that the user properly answers the security question prior to resetting their password and sending the new password to the e-mail address of record.
Architecture and Design
 Never allow the user to control what e-mail address the new password will be sent to in the password recovery mechanism.
Architecture and Design
 Assign a new temporary password rather than revealing the original password.


Related CWETypeViewChain
CWE-640 ChildOf CWE-903 Category CWE-888  

Demonstrative Examples

Observed Examples

  1. : A famous example of this type of weakness being exploited 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.

For more examples, refer to CVE relations in the bottom box.

White Box Definitions

Black Box Definitions

Taxynomy Mappings

Insufficient Password Recovery


  1. Michael Howard David LeBlanc John Viega .24 Deadly Sins of Software Security. McGraw-Hill. Section:'"Sin 19: Use of Weak Password-Based Systems." Page 279'. Published on 2010.

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