CWE-759 Variant Incomplete

Use of a One-Way Hash without a Salt

This vulnerability occurs when a system uses a one-way hash function (like MD5 or SHA-256) to protect sensitive data like passwords, but fails to add a unique random value called a salt before…

Definition

What is CWE-759?

This vulnerability occurs when a system uses a one-way hash function (like MD5 or SHA-256) to protect sensitive data like passwords, but fails to add a unique random value called a salt before hashing.
Without a salt, identical passwords produce identical hash values. This allows attackers to use pre-computed tables of common password hashes, known as rainbow tables, to quickly reverse the hash and discover the original password. Salting ensures every hash is unique, even for identical passwords, rendering these pre-computed attacks ineffective. However, it's important to understand that salting alone is not a complete defense against determined attackers with significant resources, like cloud computing or specialized hardware. While it prevents rainbow table attacks, it doesn't significantly slow down targeted brute-force or dictionary attacks if the underlying hash function is fast to compute. For true password security, a salt must be combined with intentionally slow, adaptive hash functions designed for password storage (like bcrypt, scrypt, or Argon2), as detailed in CWE-916.
Real-world impact

Real-world CVEs caused by CWE-759

  • 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.

How attackers exploit it

Step-by-step attacker path

  1. 1

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

  2. 2

    This code relies exclusively on a password mechanism (CWE-309) using only one factor of authentication (CWE-308). If an attacker can steal or guess a user's password, they are given full access to their account. Note this code also uses SHA-1, which is a weak hash (CWE-328). It also does not use a salt (CWE-759).

  3. 3

    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.

  4. 4

    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.

  5. 5

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

Vulnerable code example

Vulnerable C

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

Vulnerable C 
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();
  	}
  }
Secure code example

Secure Python

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

Secure Python 
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)
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist

How to prevent CWE-759

  • 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.
  • 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.
  • 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.
Detection signals

How to detect CWE-759

Automated Static Analysis - Binary or Bytecode SOAR Partial

According to SOAR [REF-1479], 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

Manual Static Analysis - Binary or Bytecode SOAR Partial

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Cost effective for partial coverage: ``` Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Manual Static Analysis - Source Code High

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Highly cost effective: ``` Focused Manual Spotcheck - Focused manual analysis of source Manual Source Code Review (not inspections)

Automated Static Analysis - Source Code High

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Highly cost effective: ``` Source code Weakness Analyzer Context-configured Source Code Weakness Analyzer

Automated Static Analysis SOAR Partial

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Cost effective for partial coverage: ``` Configuration Checker

Architecture or Design Review High

According to SOAR [REF-1479], 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.)

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Frequently asked questions

Frequently asked questions

What is CWE-759?

This vulnerability occurs when a system uses a one-way hash function (like MD5 or SHA-256) to protect sensitive data like passwords, but fails to add a unique random value called a salt before hashing.

How serious is CWE-759?

MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.

What languages or platforms are affected by CWE-759?

MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.

How can I prevent CWE-759?

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,…

How does Plexicus detect and fix CWE-759?

Plexicus's SAST engine matches the data-flow signature for CWE-759 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-759?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/759.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-759

CWE-916 Parent

Use of Password Hash With Insufficient Computational Effort

This vulnerability occurs when a system protects passwords by hashing them, but uses a hashing algorithm that is too fast or…

CWE-760 Sibling

Use of a One-Way Hash with a Predictable Salt

This vulnerability occurs when an application uses a one-way hash (like for password storage) but combines it with a predictable or easily…

Resources

Further reading

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