Password Brute Forcing |
| Attack Pattern ID: 49 (Standard Attack Pattern Completeness: Complete) | Typical Severity: High | Status: Draft |
DescriptionSummary
In this attack, the attacker tries every possible value for a password until they succeed. A brute force attack, if feasible computationally, will always be successful because it will essentially go through all possible passwords given the alphabet used (lower case letters, upper case letters, numbers, symbols, etc.) and the maximum length of the password.
A system will be particularly vulnerable to this type of an attack if it does not have a proper enforcement mechanism in place to ensure that passwords selected by users are strong passwords that comply with an adequate password policy.
In practice a pure brute force attack on passwords is rarely used, unless the password is suspected to be weak. Other password cracking methods exist that are far more effective (e.g. dictionary attacks, rainbow tables, etc.).
Attack Execution Flow
Determine application's/system's password policy:
Determine the password policies of the target application/system.
Attack Step Techniques
ID Attack Step Technique Description Environments 1 Determine minimum and maximum allowed password lengths.
env-All2 Determine format of allowed passwords (whether they are required or allowed to contain numbers, special characters, etc.).
env-All3 Determine account lockout policy (a strict account lockout policy will prevent brute force attacks).
env-AllIndicators
ID type Indicator Description Environments 1 Positive Passwords are used in the application/system
env-All2 Inconclusive Passwords are not used for authentication; however, brute forcing of other protection mechanisms may also be possible.
env-All
Brute force password:
Given the finite space of possible passwords dictated by the password policy determined in the previous step, try all possible passwords for a known user ID until application/system grants access.
Attack Step Techniques
ID Attack Step Technique Description Environments 1 Manually or automatically enter all possible passwords through the application/system's interface. In most systems, start with the shortest and simplest possible passwords, because most users tend to select such passwords if allowed to do so.
env-All2 Perform an offline dictionary attack or a rainbow table attack against a known password hash.
env-AllIndicators
ID type Indicator Description Environments 1 Positive Weak passwords allowed, and no account lockout policy enforced.
env-All2 Positive Password hashes can be captured by attacker.
env-All3 Negative Accounts locked out after small number of failed authentication attempts.
env-AllOutcomes
ID type Outcome Description 1 Success Attacker determines correct password for a user ID and obtains access to application or system.2 Failure Attacker is unable to determine correct password for a user ID and obtain access to application or system.3 Failure Attacker locks out account while attempting to brute force its password.Security Controls
ID type Security Control Description 1 Detective Large number of authentication failures in logs.2 Preventative Enforce strict account lockout policies.3 Preventative Enforce strong passwords (having sufficient length and containing mix of lower case and upper case letters, numbers, and special characters)4 Corrective Deny login attempts from sources that produce too many failed attempts. Note that this may cause problems where many users may have the same "source" as far as the application/system is concerned (e.g. a lot of users behind a NAT device).
Attack PrerequisitesAn attacker needs to know a username to target.
The system uses password based authentication as the one factor authentication mechanism.
An application does not have a password throttling mechanism in place. A good password throttling mechanism will make it almost impossible computationally to brute force a password as it may either lock out the user after a certain number of incorrect attempts or introduce time out periods. Both of these would make a brute force attack impractical.
Typical Likelihood of ExploitLikelihood: Medium
Methods of Attack- Brute Force
Examples-InstancesDescription
A system does not enforce a strong password policy and the user picks a five letter password consisting of lower case english letters only. The system does not implement any password throttling mechanism. Assuming the attacker does not know the length of the users' password, an attacker can brute force this password in maximum 1+26+26^2+26^3+26^4+26^5 = 1 + 26 + 676 + 17576 + 456976 + 11,881,376 = 12,356,631 attempts, and half these tries (6,178,316) on average. Using modern hardware this attack is trivial. If the attacker were to assume that the user password could also contain upper case letters (and it was case sensitive) and/or numbers, than the number of trials would have been larger.
An attacker's job would' have most likely been even easier because many users who choose easy to brute force passwords like this are also likely to use a word that can be found in the dictionary. Since there are far fewer valid english words containing up to five letters than 12,356,631, an attack that tries each of the entries in the english dictionary would go even faster.
Description
A weakness exists in the automatic password generation routine of Mailman prior to 2.1.5 that causes only about five million different passwords to be generated. This makes it easy to brute force the password for all users who decided to let Mailman automatically generate their passwords for them. Users who chose their own passwords during the sign up process would not have been affected (assuming that they chose strong passwords).
Related Vulnerabilities
CVE-2004-1143
Attacker Skills or Knowledge RequiredSkill or Knowledge Level: Low
A brute force attack is very straightforward. A variety of password cracking tools are widely available.
Resources RequiredA powerful enough computer for the job with sufficient CPU, RAM and HD. Exact requirements will depend on the size of the brute force job and the time requirement for completion. Some brute forcing jobs may require grid or distributed computing (e.g. DES Challenge).
Indicators-Warnings of AttackMany incorrect login attempts are detected by the system.
Obfuscation TechniquesTry to spoof IP addresses so that it does not look like the incorrect log in attempts are coming from the same computer.
Solutions and MitigationsImplement a password throttling mechanism. This mechanism should take into account both the IP address and the log in name of the user.
Put together a strong password policy and make sure that all user created passwords comply with it. Alternatively automatically generate strong passwords for users.
Passwords need to be recycled to prevent aging, that is every once in a while a new password must be chosen.
Attack Motivation-Consequences- Privilege Escalation
Related Weaknesses Related Attack Patterns| Nature | Type | ID | Name | Description | View(s) this relationship pertains to |
|---|---|---|---|---|---|
| ChildOf |  Attack Pattern | 112 | Brute Force | Mechanism of Attack (primary)1000 | |
| ParentOf | Attack Pattern | 16 | Dictionary-based Password Attack | Mechanism of Attack1000 | |
| ParentOf | Attack Pattern | 55 | Rainbow Table Password Cracking | Mechanism of Attack1000 | |
| ParentOf | Attack Pattern | 70 | Try Common(default) Usernames and Passwords | Mechanism of Attack (primary)1000 |
Purposes- Penetration
CIA Impact Technical Context| Architectural Paradigms | All |
|---|---|
| Frameworks | All |
| Platforms | All |
| Languages | All |
Content History| Submissions | ||||
|---|---|---|---|---|
| Submitter | Organization | Date | ||
| Eugene Lebanidze | Cigital, Inc | 2007-02-26 | ||
| Modifications | |||||
|---|---|---|---|---|---|
| Modifier | Organization | Date | Comments | ||
| Sean Barnum | Cigital, Inc | 2007-03-01 | Review and revision of content | ||
| Richard Struse | VOXEM, Inc | 2007-03-26 | Review and feedback leading to changes in Description and Related Attack Patterns | ||
| Sean Barnum | Cigital, Inc | 2007-04-13 | Modified pattern content according to review and feedback | ||
| Amit Sethi | Cigital, Inc. | 2007-10-29 | Added extended Attack Execution Flow | ||
