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CWE-640 Individual Dictionary Definition (Draft 9)
Weakness ID
| Status: Incomplete 640 (Weakness Base) | | Description | Summary 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. | | Likelihood of Exploit | High | | Common Consequences | An attacker gains unauthorized access to the system by retrieving legitimate user's authentication credentials An attacker denies 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. | | 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.
| | Potential Mitigations |
Make sure that all input supplied by the user to the password recovery mechanism is thoroughly filtered and validated
Do not use standard weak security questions and use several security questions.
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.
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.
Never allow the user to control what e-mail address the new password will be sent to in the password recovery mechanism.
Assign a new temporary password rather than revealing the original password.
| | Observed Examples | | Reference | Description |
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| 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. |
| | Relationships | | | Applicable Platforms | All | | Time of Introduction | Architecture and Design Implementation |
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- Weakness
- Base
- Variant
- Class
- Chain
- Composite
- Category
- View
- Deprecated
