Use of a One-Way Hash without a Salt

Opis

The product uses a one-way cryptographic hash against an input that should not be reversible, such as a password, but the product does not also use a 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.

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.

Skutki

• Access Control

  Bypass Protection Mechanism; Gain Privileges or Assume Identity

  If an attacker can gain access to the hashes, then the lack of a salt makes it easier to conduct brute force attacks using techniques such as rainbow tables.

Zapobieganie

• 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.

  Skuteczność: High

• Architecture and Design

  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.

  Skuteczność: Limited

• 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.

Przykłady podatności

• CVE-2008-1526 Router does not use a salt with a hash, making it easier to crack passwords.
• CVE-2006-1058 Router does not use a salt with a hash, making it easier to crack passwords.

Słabość nadrzędna

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

Kiedy powstaje

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

Dotyczy

Not Language-Specific

Źródła

1. bcrypt — Johnny Shelley
2. Tarsnap - The scrypt key derivation function and encryption utility — Colin Percival
3. RFC2898 - PKCS #5: Password-Based Cryptography Specification Version 2.0 — B. Kaliski, 5.2 PBKDF2, 2000
4. How To Safely Store A Password — Coda Hale, 2010
5. How Companies Can Beef Up Password Security (interview with Thomas H. Ptacek) — Brian Krebs, 2012
6. Password security: past, present, future — Solar Designer, 2012
7. Our password hashing has no clothes — Troy Hunt, 2012
8. Should we really use bcrypt/scrypt? — Joshbw, 2012
9. Password Storage Cheat Sheet — OWASP
10. Enough With The Rainbow Tables: What You Need To Know About Secure Password Schemes — Thomas Ptacek, 2007
11. The Importance of Being Canonical — Robert Graham, 2009
12. Password Hashing — James McGlinn
13. Rainbow Hash Cracking — Jeff Atwood, 2007
14. Speed Hashing — Jeff Atwood, 2012
15. Rainbow table — Wikipedia, 2009
16. Writing Secure Code — Michael Howard, David LeBlanc, Chapter 9, "Creating a Salted Hash" Page 302, Microsoft Press, 2002
17. The Art of Software Security Assessment — Mark Dowd, John McDonald, Justin Schuh, Chapter 2, "Salt Values", Page 46, Addison Wesley, 2006
18. State-of-the-Art Resources (SOAR) for Software Vulnerability Detection, Test, and Evaluation — Gregory Larsen, E. Kenneth Hong Fong, David A. Wheeler, Rama S. Moorthy, 2014