Détail du CWE-760

The product uses a one-way cryptographic hash against an input that should not be reversible, such as a password, but the product uses a predictable salt as part of the input.

This makes it easier for attackers to pre-compute the hash value using dictionary attack techniques such as rainbow tables, effectively disabling the protection that an unpredictable salt would provide.

It should be noted that, despite common perceptions, the use of a good salt with a hash does not sufficiently increase the effort for an attacker who is targeting an individual password, or who has a large amount of computing resources available, such as with cloud-based services or specialized, inexpensive hardware. Offline password cracking can still be effective if the hash function is not expensive to compute; many cryptographic functions are designed to be efficient and can be vulnerable to attacks using massive computing resources, even if the hash is cryptographically strong. The use of a salt only slightly increases the computing requirements for an attacker compared to other strategies such as adaptive hash functions. See CWE-916 for more details.

Informations de base

In cryptography, salt refers to some random addition of data to an input before hashing to make dictionary attacks more difficult.

Modes d'introduction

Implementation : REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Conséquences courantes

Exemples observés

Mesures d’atténuation potentielles

Phases : 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 [REF-291], scrypt [REF-292], and PBKDF2 [REF-293]. 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.

Phases : Implementation
If a technique that requires extra computational effort can not be implemented, then for each password that is processed, generate a new random salt using a strong random number generator with unpredictable seeds. Add the salt to the plaintext password before hashing it. When storing the hash, also store the salt. Do not use the same salt for every password.

Méthodes de détection

Automated Static Analysis

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
Efficacité : High

Notes de cartographie des vulnérabilités

Justification : This CWE entry is at the Variant level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Commentaire : Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

NotesNotes

As of CWE 4.5, terminology related to randomness, entropy, and predictability can vary widely. Within the developer and other communities, "randomness" is used heavily. However, within cryptography, "entropy" is distinct, typically implied as a measurement. There are no commonly-used definitions, even within standards documents and cryptography papers. Future versions of CWE will attempt to define these terms and, if necessary, distinguish between them in ways that are appropriate for different communities but do not reduce the usability of CWE for mapping, understanding, or other scenarios.

Références

REF-291

bcrypt
Johnny Shelley.
http://bcrypt.sourceforge.net/

REF-292

Tarsnap - The scrypt key derivation function and encryption utility
Colin Percival.
http://www.tarsnap.com/scrypt.html

REF-293

RFC2898 - PKCS #5: Password-Based Cryptography Specification Version 2.0
B. Kaliski.
https://www.rfc-editor.org/rfc/rfc2898

REF-294

How To Safely Store A Password
Coda Hale.
https://codahale.com/how-to-safely-store-a-password/

REF-295

How Companies Can Beef Up Password Security (interview with Thomas H. Ptacek)
Brian Krebs.
https://krebsonsecurity.com/2012/06/how-companies-can-beef-up-password-security/

REF-296

Password security: past, present, future
Solar Designer.
https://www.openwall.com/presentations/PHDays2012-Password-Security/

REF-297

Our password hashing has no clothes
Troy Hunt.
https://www.troyhunt.com/our-password-hashing-has-no-clothes/

REF-298

Should we really use bcrypt/scrypt?
Joshbw.
https://web.archive.org/web/20120629144851/http://www.analyticalengine.net/2012/06/should-we-really-use-bcryptscrypt/

REF-631

Password Storage Cheat Sheet
OWASP.
https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html

REF-632

Enough With The Rainbow Tables: What You Need To Know About Secure Password Schemes
Thomas Ptacek.
http://hashphp.org/hashing.html

REF-633

The Importance of Being Canonical
Robert Graham.
https://blog.erratasec.com/2009/02/importance-of-being-canonical.html#.ZCbyY7LMJPY

REF-634

Password Hashing
James McGlinn.
https://privacyaustralia.net/phpsec/articles/password-hashing/

REF-635

Rainbow Hash Cracking
Jeff Atwood.
https://blog.codinghorror.com/rainbow-hash-cracking/

REF-636

Speed Hashing
Jeff Atwood.
https://blog.codinghorror.com/speed-hashing/

REF-637

Rainbow table
https://en.wikipedia.org/wiki/Rainbow_table

REF-7

Writing Secure Code
Michael Howard, David LeBlanc.
https://www.microsoftpressstore.com/store/writing-secure-code-9780735617223

REF-62

The Art of Software Security Assessment
Mark Dowd, John McDonald, Justin Schuh.

Soumission

Modifications