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ID

CWE-916: Use of Password Hash With Insufficient Computational Effort

Weakness ID: 916
Abstraction: Base
Status: Incomplete
Presentation Filter:
+ Description

Description Summary

The software generates a hash for a password, but it uses a scheme that does not provide a sufficient level of computational effort that would make password cracking attacks infeasible or expensive.

Extended Description

Many password storage mechanisms compute a hash and store the hash, instead of storing the original password in plaintext. In this design, authentication involves accepting an incoming password, computing its hash, and comparing it to the stored hash.

Many hash algorithms are designed to execute quickly with minimal overhead, even cryptographic hashes. However, this efficiency is a problem for password storage, because it can reduce an attacker's workload for brute-force password cracking. If an attacker can obtain the hashes through some other method (such as SQL injection on a database that stores hashes), then the attacker can store the hashes offline and use various techniques to crack the passwords by computing hashes efficiently. Without a built-in workload, modern attacks can compute large numbers of hashes, or even exhaust the entire space of all possible passwords, within a very short amount of time, using massively-parallel computing (such as cloud computing) and GPU, ASIC, or FPGA hardware. In such a scenario, an efficient hash algorithm helps the attacker.

There are several properties of a hash scheme that are relevant to its strength against an offline, massively-parallel attack:

  • The amount of CPU time required to compute the hash ("stretching")

  • The amount of memory required to compute the hash ("memory-hard" operations)

  • Including a random value, along with the password, as input to the hash computation ("salting")

  • Given a hash, there is no known way of determining a password that produces this hash value, other than by guessing possible passwords ("one-way" hashing)

  • Relative to the number of all possible hashes that can be generated by the scheme, there is a low likelihood of producing the same hash for multiple different inputs ("collision resistance")

Note that the security requirements for the software may vary depending on the environment and the value of the passwords. Different schemes might not provide all of these properties, yet may still provide sufficient security for the environment. Conversely, a solution might be very strong in preserving one property, which still being very weak for an attack against another property, or it might not be able to significantly reduce the efficiency of a massively-parallel attack.

+ Time of Introduction
  • Architecture and Design
+ Applicable Platforms

Languages

Language-independent

+ Common Consequences
ScopeEffect
Access Control

Technical Impact: Bypass protection mechanism; Gain privileges / assume identity

If an attacker can gain access to the hashes, then the lack of sufficient computational effort will make it easier to conduct brute force attacks using techniques such as rainbow tables, or specialized hardware such as GPUs, which can be much faster than general-purpose CPUs for computing hashes.

+ Detection Methods

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Bytecode Weakness Analysis - including disassembler + source code weakness analysis

  • Binary Weakness Analysis - including disassembler + source code weakness analysis

Effectiveness: SOAR Partial

Manual Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Effectiveness: SOAR Partial

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Focused Manual Spotcheck - Focused manual analysis of source

  • Manual Source Code Review (not inspections)

Effectiveness: SOAR High

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Source code Weakness Analyzer

  • Context-configured Source Code Weakness Analyzer

Effectiveness: SOAR High

Automated Static Analysis

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:

  • Configuration Checker

Effectiveness: SOAR Partial

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Highly cost effective:

  • Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

  • Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

Effectiveness: SOAR High

+ Observed Examples
ReferenceDescription
Router does not use a salt with a hash, making it easier to crack passwords.
Router does not use a salt with a hash, making it easier to crack passwords.
Blogging software uses a hard-coded salt when calculating a password hash.
Database server uses the username for a salt when encrypting passwords, simplifying brute force attacks.
Server uses a constant salt when encrypting passwords, simplifying brute force attacks.
chain: product generates predictable MD5 hashes using a constant value combined with username, allowing authentication bypass.
+ Potential Mitigations

Phase: Architecture and Design

Use an adaptive hash function that can be configured to change the amount of computational effort needed to compute the hash, such as the number of iterations ("stretching") or the amount of memory required. Some hash functions perform salting automatically. These functions can significantly increase the overhead for a brute force attack compared to intentionally-fast functions such as MD5. For example, rainbow table attacks can become infeasible due to the high computing overhead. Finally, since computing power gets faster and cheaper over time, the technique can be reconfigured to increase the workload without forcing an entire replacement of the algorithm in use.

Some hash functions that have one or more of these desired properties include bcrypt [R.916.1], scrypt [R.916.2], and PBKDF2 [R.916.3]. While there is active debate about which of these is the most effective, they are all stronger than using salts with hash functions with very little computing overhead.

Note that using these functions can have an impact on performance, so they require special consideration to avoid denial-of-service attacks. However, their configurability provides finer control over how much CPU and memory is used, so it could be adjusted to suit the environment's needs.

Effectiveness: High

Phases: Implementation; Architecture and Design

When using industry-approved techniques, use them correctly. Don't cut corners by skipping resource-intensive steps (CWE-325). These steps are often essential for preventing common attacks.

+ Weakness Ordinalities
OrdinalityDescription
Primary
(where the weakness exists independent of other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness BaseWeakness Base327Use of a Broken or Risky Cryptographic Algorithm
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base759Use of a One-Way Hash without a Salt
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base760Use of a One-Way Hash with a Predictable Salt
Development Concepts (primary)699
Research Concepts (primary)1000
+ References
[R.916.1] [REF-45] Johnny Shelley. "bcrypt". <http://bcrypt.sourceforge.net/>.
[R.916.2] [REF-39] Colin Percival. "Tarsnap - The scrypt key derivation function and encryption utility". <http://www.tarsnap.com/scrypt.html>.
[R.916.3] [REF-40] B. Kaliski. "RFC2898 - PKCS #5: Password-Based Cryptography Specification Version 2.0". 5.2 PBKDF2. 2000. <http://tools.ietf.org/html/rfc2898>.
[REF-38] Coda Hale. "How To Safely Store A Password". 2010-01-31. <http://codahale.com/how-to-safely-store-a-password/>.
[REF-41] Brian Krebs. "How Companies Can Beef Up Password Security (interview with Thomas H. Ptacek)". 2012-06-11. <http://krebsonsecurity.com/2012/06/how-companies-can-beef-up-password-security/>.
[REF-42] Solar Designer. "Password security: past, present, future". 2012. <http://www.openwall.com/presentations/PHDays2012-Password-Security/>.
[REF-43] Troy Hunt. "Our password hashing has no clothes". 2012-06-26. <http://www.troyhunt.com/2012/06/our-password-hashing-has-no-clothes.html>.
[REF-44] Joshbw. "Should we really use bcrypt/scrypt?". 2012-06-08. <http://www.analyticalengine.net/2012/06/should-we-really-use-bcryptscrypt/>.
Jeff Atwood. "Speed Hashing". 2012-04-06. <http://www.codinghorror.com/blog/2012/04/speed-hashing.html>.
OWASP. "Password Storage Cheat Sheet". <https://www.owasp.org/index.php/Password_Storage_Cheat_Sheet>.
Thomas Ptacek. "Enough With The Rainbow Tables: What You Need To Know About Secure Password Schemes". 2007-09-10. <http://www.securityfocus.com/blogs/262>.
Solar Designer. "Password hashing at scale". October 1, 2012. <http://www.openwall.com/presentations/YaC2012-Password-Hashing-At-Scale/>.
Solar Designer. "New developments in password hashing: ROM-port-hard functions". November, 2012. <http://www.openwall.com/presentations/ZeroNights2012-New-In-Password-Hashing/>.
Robert Graham. "The Importance of Being Canonical". 2009-02-02. <http://erratasec.blogspot.com/2009/02/importance-of-being-canonical.html>.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
2013-01-28MITREInternal CWE Team
Created with input from members of the secure password hashing community.
Modifications
Modification DateModifierOrganizationSource
2014-02-18CWE Content TeamMITREInternal
updated Potential_Mitigations, References
2014-07-30CWE Content TeamMITREInternal
updated Detection_Factors
2017-01-19CWE Content TeamMITREInternal
updated Relationships

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Page Last Updated: January 18, 2017