Use of Weak Hash

The product uses an algorithm that produces a digest (output value) that does not meet security expectations for a hash function that allows an adversary to reasonably determine the original input (preimage attack), find another input that can produce the same hash (2nd preimage attack), or find multiple inputs that evaluate to the same hash (birthday attack).


A hash function is defined as an algorithm that maps arbitrarily sized data into a fixed-sized digest (output) such that the following properties hold:

The algorithm is not invertible (also called "one-way" or "not reversible")

The algorithm is deterministic; the same input produces the same digest every time

Building on this definition, a cryptographic hash function must also ensure that a malicious actor cannot leverage the hash function to have a reasonable chance of success at determining any of the following:

the original input (preimage attack), given only the digest

another input that can produce the same digest (2nd preimage attack), given the original input

a set of two or more inputs that evaluate to the same digest (birthday attack), given the actor can arbitrarily choose the inputs to be hashed and can do so a reasonable amount of times

What is regarded as "reasonable" varies by context and threat model, but in general, "reasonable" could cover any attack that is more efficient than brute force (i.e., on average, attempting half of all possible combinations). Note that some attacks might be more efficient than brute force but are still not regarded as achievable in the real world.

Any algorithm does not meet the above conditions will generally be considered weak for general use in hashing.

In addition to algorithmic weaknesses, a hash function can be made weak by using the hash in a security context that breaks its security guarantees. For example, using a hash function without a salt for storing passwords (that are sufficiently short) could enable an adversary to create a "rainbow table" [REF-637] to recover the password under certain conditions; this attack works against such hash functions as MD5, SHA-1, and SHA-2.


The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

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())) {
String plainText = new String(plainTextIn);
MessageDigest encer = MessageDigest.getInstance("SHA");
byte[] digest = password.digest();
//Login if hash matches stored hash
if (equal(digest,secret_password())) {

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).

See Also

OWASP Top Ten 2021 Category A02:2021 - Cryptographic Failures

Weaknesses in this category are related to the A02 category "Cryptographic Failures" in the OWASP Top Ten 2021.

OWASP Top Ten 2017 Category A3 - Sensitive Data Exposure

Weaknesses in this category are related to the A3 category in the OWASP Top Ten 2017.

Encrypt Data

Weaknesses in this category are related to the design and architecture of data confidentiality in a system. Frequently these deal with the use of encryption libraries....

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Entries with Maintenance Notes

CWE entries in this view have maintenance notes. Maintenance notes are an indicator that an entry might change significantly in future versions. This view was created...

Weaknesses without Software Fault Patterns

CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...

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