CVE-2011-2686 in Ruby
Summary
by MITRE
Ruby before 1.8.7-p352 does not reset the random seed upon forking, which makes it easier for context-dependent attackers to predict the values of random numbers by leveraging knowledge of the number sequence obtained in a different child process, a related issue to CVE-2003-0900. NOTE: this issue exists because of a regression during Ruby 1.8.6 development.
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Analysis
by VulDB Data Team • 11/17/2021
The vulnerability described in CVE-2011-2686 represents a critical weakness in the Ruby programming language's handling of random number generation during process forking operations. This flaw specifically affects Ruby versions prior to 1.8.7-p352 and stems from a regression introduced during the development of Ruby 1.8.6. The core issue lies in the improper management of the random seed state when a parent process creates child processes through forking mechanisms, creating persistent security implications that extend beyond the immediate execution context.
The technical flaw manifests when Ruby applications utilize the fork() system call to create child processes while relying on random number generation for security-sensitive operations. During normal operation, Ruby's random number generator maintains an internal state that should be properly initialized or reseeded when new processes are created. However, due to the regression in Ruby 1.8.6, the random seed value persists across the fork boundary, meaning that child processes inherit the same random state as their parent. This inheritance creates a predictable pattern where attackers can potentially determine the sequence of random numbers generated in one process and use that knowledge to predict values in other processes, fundamentally compromising the entropy and security guarantees of the random number generation.
The operational impact of this vulnerability extends beyond simple predictability issues, as it creates a pathway for context-dependent attackers to exploit security-sensitive applications that rely on random number generation for cryptographic operations, session management, or other security-critical functions. When applications fork processes for parallel execution or to handle concurrent requests, the persistence of random seed values across these process boundaries enables attackers to reconstruct the random number sequence, potentially leading to session hijacking, cryptographic key prediction, or other security breaches. This vulnerability is particularly dangerous in web applications, network services, and any system where predictable random numbers could be exploited to compromise security controls. The issue is categorized under CWE-330 as "Use of Insufficiently Random Values" and aligns with ATT&CK technique T1083 for discovering system information and T1566 for credential access through predictable values.
The root cause of this regression demonstrates the complexity of managing cryptographic state across process boundaries and highlights the importance of proper state initialization in multi-process environments. When a parent process generates random numbers and then forks, each child should ideally begin with a fresh random seed to maintain cryptographic security properties. However, the Ruby implementation failed to reset this critical state variable during the forking process, creating a persistent vulnerability that affects all applications running on affected Ruby versions. This regression represents a failure in the security testing and validation processes during the Ruby 1.8.6 development cycle, where the change in behavior was not properly identified as a security risk. Organizations running Ruby applications should prioritize upgrading to Ruby 1.8.7-p352 or later versions to resolve this vulnerability, while also implementing additional monitoring and validation of random number generation in their applications to detect any potential exploitation attempts.