CWE-759

ソルトなしの一方向ハッシュの使用

Use of a One-Way Hash without a Salt

脆弱性作成中

日本語説明

この製品は、パスワードのような可逆的であってはならない入力に対して一方向暗号ハッシュを使用するが、入力の一部としてソルトも使用しない。

これにより、攻撃者はレインボーテーブルのような辞書攻撃テクニックを使ってハッシュ値を事前に計算することが容易になる。

一般的な認識とは裏腹に、ハッシュとともに優れたソルトを使用することは、個々のパスワードをターゲットにしている攻撃者や、クラウドベースのサービスや特殊で安価なハードウェアなど、大量のコンピューティングリソースを利用できる攻撃者の労力を十分に増加させるものではないことに留意すべきである。多くの暗号関数は効率的に設計されているため、ハッシュが暗号的に強力であっても、大規模なコンピューティングリソースを使用する攻撃に対して脆弱になる可能性があります。多くの暗号関数は効率的に設計されており、ハッシュが暗号的に強力であっても、膨大な計算資源を使用する攻撃には脆弱である。ソルトの使用は、適応型ハッシュ関数などの他の戦略と比較して、攻撃者の計算要件をわずかに増加させるだけである。詳細はCWE-916を参照。

原文 (English)

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.

関連する脆弱性

想定される影響

Scope: Access Control / Impact: Bypass Protection Mechanism; Gain Privileges or Assume Identity

対策・緩和策

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.

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.

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.

外部リンク

MITRE公式ページ — CWE-759