CVE-2019-5420

A remote code execution vulnerability in development mode Rails <5.2.2.1, <6.0.0.beta3 can allow an attacker to guess the automatically generated development mode secret token. This secret token can be used in combination with other Rails internals to escalate to a remote code execution exploit.

Weakness

The product uses insufficiently random numbers or values in a security context that depends on unpredictable numbers.

Affected Software

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

References

• http://packetstormsecurity.com/files/152704/Ruby-On-Rails-DoubleTap-Development-Mode-secret_key_base-Remote-Code-Execution.html
• https://groups.google.com/forum/#%21topic/rubyonrails-security/IsQKvDqZdKw
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/Y43636TH4D6T46IC6N2RQVJTRFJAAYGA/
• https://weblog.rubyonrails.org/2019/3/13/Rails-4-2-5-1-5-1-6-2-have-been-released/
• https://www.exploit-db.com/exploits/46785/