CWE - CWE-640: Weak Password Recovery Mechanism for Forgotten Password (4.19.1)
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  • CWE-640: Weak Password Recovery Mechanism for Forgotten Password

    Weakness ID: 640
    Vulnerability Mapping: ALLOWED This CWE ID could be used to map to real-world vulnerabilities in limited situations requiring careful review (with careful review of mapping notes)
    Abstraction: Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
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    + Description
    The product 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. Weak password recovery schemes completely undermine a strong password authentication scheme.

    This weakness may be that the security question is too easy to guess or find an answer to (e.g. because the question is too common, or the answers can be found using social media). 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.

    + Common Consequences
    Section HelpThis table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
    Impact Details

    Gain Privileges or Assume Identity

    Scope: Access Control

    An attacker could gain unauthorized access to the system by retrieving legitimate user's authentication credentials.

    DoS: Resource Consumption (Other)

    Scope: Availability

    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.

    Other

    Scope: Integrity, Other

    The system's security functionality is turned against the system by the attacker.
    + Potential Mitigations
    Phase(s) Mitigation

    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.
    + Relationships
    Section Help This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.
    + Relevant to the view "Research Concepts" (View-1000)
    Nature Type ID Name
    ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 1390 Weak Authentication
    + Relevant to the view "Software Development" (View-699)
    Nature Type ID Name
    MemberOf Category Category - a CWE entry that contains a set of other entries that share a common characteristic. 255 Credentials Management Errors
    MemberOf Category Category - a CWE entry that contains a set of other entries that share a common characteristic. 840 Business Logic Errors
    + Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (View-1003)
    Nature Type ID Name
    ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 287 Improper Authentication
    + Relevant to the view "Architectural Concepts" (View-1008)
    Nature Type ID Name
    MemberOf Category Category - a CWE entry that contains a set of other entries that share a common characteristic. 1010 Authenticate Actors
    + Modes Of Introduction
    Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
    Phase Note
    Architecture and Design COMMISSION: This weakness refers to an incorrect design related to an architectural security tactic.
    Implementation
    + Applicable Platforms
    Section HelpThis listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.
    Languages

    Class: Not Language-Specific (Undetermined Prevalence)

    + Likelihood Of Exploit
    High
    + Demonstrative Examples

    Example 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.



    + Weakness Ordinalities
    Ordinality Description
    Primary
    (where the weakness exists independent of other weaknesses)
    + Memberships
    Section HelpThis MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
    Nature Type ID Name
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 724 OWASP Top Ten 2004 Category A3 - Broken Authentication and Session Management
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 930 OWASP Top Ten 2013 Category A2 - Broken Authentication and Session Management
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 959 SFP Secondary Cluster: Weak Cryptography
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1028 OWASP Top Ten 2017 Category A2 - Broken Authentication
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1353 OWASP Top Ten 2021 Category A07:2021 - Identification and Authentication Failures
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1396 Comprehensive Categorization: Access Control
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1442 OWASP Top Ten 2025 Category A07:2025 - Authentication Failures
    + Vulnerability Mapping Notes
    Usage ALLOWED-WITH-REVIEW
    (this CWE ID could be used to map to real-world vulnerabilities in limited situations requiring careful review)
    Reason Frequent Misuse

    Rationale

    This entry appears to be frequently misused for any weakness related to password changes, even though the name focuses on "Password Recovery" for a "forgotten" password.

    Comments

    CWE-640 should only be used when there is a "password recovery" mechanism for forgotten passwords. Consider password-related entries under CWE-1390: Weak Authentication.
    + Notes

    Maintenance

    This entry might be reclassified as a category or "loose composite," since it lists multiple specific errors that can make the mechanism weak. However, under view 1000, it could be a weakness under protection mechanism failure, although it is different from most PMF issues since it is related to a feature that is designed to bypass a protection mechanism (specifically, the lack of knowledge of a password).

    Maintenance

    This entry probably needs to be split; see extended description.
    + Taxonomy Mappings
    Mapped Taxonomy Name Node ID Fit Mapped Node Name
    WASC 49 Insufficient Password Recovery
    + References
    [REF-44] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 19: Use of Weak Password-Based Systems." Page 279. McGraw-Hill. 2010.
    + Content History
    + Submissions
    Submission Date Submitter Organization
    2008-01-30
    (CWE Draft 8, 2008-01-30)
    Evgeny Lebanidze Cigital
    + Modifications
    Modification Date Modifier Organization
    2025-12-11
    (CWE 4.19, 2025-12-11)
    CWE Content Team MITRE
    updated Relationships, Weakness_Ordinalities
    2023-06-29 CWE Content Team MITRE
    updated Mapping_Notes
    2023-04-27 CWE Content Team MITRE
    updated Relationships
    2023-01-31 CWE Content Team MITRE
    updated Description
    2022-10-13 CWE Content Team MITRE
    updated Relationships
    2021-10-28 CWE Content Team MITRE
    updated Relationships
    2019-06-20 CWE Content Team MITRE
    updated Relationships
    2018-03-27 CWE Content Team MITRE
    updated Relationships
    2017-11-08 CWE Content Team MITRE
    updated Applicable_Platforms, Demonstrative_Examples, Description, Enabling_Factors_for_Exploitation, Modes_of_Introduction, Observed_Examples, Relationships
    2015-12-07 CWE Content Team MITRE
    updated Relationships
    2014-07-30 CWE Content Team MITRE
    updated Relationships
    2014-06-23 CWE Content Team MITRE
    updated Relationships
    2012-10-30 CWE Content Team MITRE
    updated Potential_Mitigations
    2012-05-11 CWE Content Team MITRE
    updated References, Relationships
    2011-06-01 CWE Content Team MITRE
    updated Common_Consequences
    2011-03-29 CWE Content Team MITRE
    updated Relationships
    2010-12-13 CWE Content Team MITRE
    updated Common_Consequences
    2010-02-16 CWE Content Team MITRE
    updated Taxonomy_Mappings
    2009-05-27 CWE Content Team MITRE
    updated Related_Attack_Patterns
    2009-03-10 CWE Content Team MITRE
    updated Relationships
    2008-09-08 CWE Content Team MITRE
    updated Common_Consequences, Description, Maintenance_Notes, Name, Relationships
    + Previous Entry Names
    Change Date Previous Entry Name
    2008-09-09 Weak Password Recovery Mechanism
    Page Last Updated: January 21, 2026