Piwigo is an open source photo gallery application for the web. In versions on the 14.x branch, when installing, the secret_key configuration parameter is set to MD5(RAND()) in MySQL. However, RAND() only has 30 bits of randomness, making it feasible to brute-force the secret key. The CSRF token is constructed partially from the secret key, and this can be used to check if the brute force succeeded. Trying all possible values takes approximately one hour. The impact of this is limited. The auto login key uses the users password on top of the secret key. The pwg token uses the users session identifier on top of the secret key. It seems that values for get_ephemeral_key can be generated when one knows the secret key. Version 15.0.0 contains a fix for the issue.
Weakness
The product uses insufficiently random numbers or values in a security context that depends on unpredictable numbers.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Piwigo | Piwigo | 14.0.0 (including) | 14.5.0 (including) |
Potential Mitigations
- Use a well-vetted algorithm that is currently considered to be strong by experts in the field, and select well-tested implementations with adequate length seeds.
- In general, if a pseudo-random number generator is not advertised as being cryptographically secure, then it is probably a statistical PRNG and should not be used in security-sensitive contexts.
- Pseudo-random number generators can produce predictable numbers if the generator is known and the seed can be guessed. A 256-bit seed is a good starting point for producing a “random enough” number.
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/112.html
- https://cwe.mitre.org/data/definitions/485.html
- https://cwe.mitre.org/data/definitions/59.html