用户工具

站点工具


cwe:cn:definition:759

CWE-759:使用未加Salt的单向哈希算法

Description Summary

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

Extended Description

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.

Background Details

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

Common Consequences

Scope Technical Impace Note
Access_ControlBypass protection mechanism
Gain privileges / 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.

Detection Methods

Detection Method - 1

Automated Static Analysis - Binary / Bytecode

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

Detection Method - 2

Manual Static Analysis - Binary / Bytecode

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

Detection Method - 3

Manual Static Analysis - Source Code

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

Detection Method - 4

Automated Static Analysis - Source Code

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

Detection Method - 5

Automated Static Analysis

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

Detection Method - 6

Architecture / Design Review

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

Potential Mitigations

Mitigation - 1

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.

2013/05/30 13:23

Mitigation - 2

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.

Mitigation - 3

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.

2013/05/30 09:37

Demonstrative Examples

Example - 1

In both of these examples, a user is logged in if their given password matches a stored password:

unsigned char *check_passwd(char *plaintext) { 
ctext = simple_digest("sha1",plaintext,strlen(plaintext), ... ); 
//Login if hash matches stored hash 
if (equal(ctext, secret_password())) { 
login_user(); 
 
} 
 
} 
String plainText = new String(plainTextIn); 
MessageDigest encer = MessageDigest.getInstance("SHA"); 
encer.update(plainTextIn); 
byte[] digest = password.digest(); 
//Login if hash matches stored hash 
if (equal(digest,secret_password())) { 
login_user(); 
 
} 

This code does not provide a salt to the hashing function, thus increasing the chances of an attacker being able to reverse the hash and discover the original password. Note this code also exhibits CWE-328 (Reversible One-Way Hash).

2013/05/30 13:23

Example - 2

In this example, a new user provides a new username and password to create an account. The program hashes the new user's password then stores it in a database.

def storePassword(userName,Password): 
hasher = hashlib.new('md5') 
hasher.update(Password) 
hashedPassword = hasher.digest() 
# UpdateUserLogin returns True on success, False otherwise 
return updateUserLogin(userName,hashedPassword) 
 

While it is good to avoid storing a cleartext password, the program does not provide a salt to the hashing function, thus increasing the chances of an attacker being able to reverse the hash and discover the original password if the database is compromised.

Fixing this is as simple as providing a salt to the hashing function on initialization:

def storePassword(userName,Password): 
hasher = hashlib.new('md5',b'SaltGoesHere') 
hasher.update(Password) 
hashedPassword = hasher.digest() 
# UpdateUserLogin returns True on success, False otherwise 
return updateUserLogin(userName,hashedPassword) 
 

Note that regardless of the usage of a salt, the md5 hash is no longer considered secure, so this example still exhibits CWE-327.

Observed Examples

Reference Description
CVE-2008-1526Router does not use a salt with a hash, making it easier to crack passwords.
CVE-2006-1058Router does not use a salt with a hash, making it easier to crack passwords.
cwe/cn/definition/759.txt · 最后更改: 2014/09/04 14:50 (外部编辑)