Source: cve@mitre.org
Perl 5.8.1 on Fedora Core does not properly initialize the random number generator when forking, which makes it easier for attackers to predict random numbers.
Perl 5.8.1 on Fedora Core suffers from a critical vulnerability where the random number generator is not properly initialized after forking, allowing attackers to predict random numbers. This flaw can be leveraged to compromise security-sensitive operations, such as cryptographic keys or session IDs, leading to unauthorized access and data breaches.
Step 1: Target Identification: The attacker identifies a Fedora Core system running Perl 5.8.1.
Step 2: Process Forking: The attacker identifies a Perl script or application that forks child processes, especially those involved in security-sensitive operations (e.g., generating session IDs, cryptographic keys, or performing authentication).
Step 3: Seed Prediction: The attacker determines the initial seed or state of the RNG in the parent process. This may involve observing the parent process's behavior or leveraging other vulnerabilities to gain information about the parent's state.
Step 4: Child Process Execution: The attacker triggers the execution of a child process.
Step 5: Random Number Prediction: The attacker uses knowledge of the RNG's initial state (inherited from the parent) to predict the output of random number generation functions in the child process.
Step 6: Exploitation: The attacker uses the predicted random numbers to bypass security measures. This could involve guessing session IDs, forging authentication tokens, or cracking cryptographic keys.
The root cause lies in the Perl interpreter's handling of the random number generator (RNG) during the fork() system call. When a process forks, it creates a child process that is a copy of the parent. If the RNG is not properly re-seeded in the child process, it inherits the same internal state as the parent. This means that subsequent calls to random number generation functions in the child will produce predictable output, as the starting point is known. The flaw specifically affects the initialization of the RNG's internal state, leading to a lack of entropy in the child process. This allows an attacker to predict the output of random number generation functions, such as rand() or functions that rely on it, like those used to generate session tokens or cryptographic keys.
Due to the age of the vulnerability, it's unlikely to be actively targeted by sophisticated APTs. However, the underlying principle of predictable RNGs is a common attack vector. This vulnerability is not listed on the CISA KEV.
Monitor system logs for unusual process creation patterns, especially involving Perl scripts that fork child processes.
Analyze network traffic for suspicious requests that might indicate attempts to guess session IDs or authentication tokens.
Examine Perl scripts for the use of random number generation functions and assess how the output is used.
Implement intrusion detection rules to identify attempts to exploit predictable random number generation.
Monitor for the use of deprecated or vulnerable Perl modules related to random number generation.
Upgrade to a patched version of Perl (5.8.2 or later) or a supported operating system.
Ensure that the random number generator is properly re-seeded in child processes after forking. This can be achieved by using a cryptographically secure random number source (e.g., /dev/urandom) to seed the RNG in the child process.
Avoid using predictable random numbers for security-sensitive operations. Use cryptographically secure random number generators (CSPRNGs) provided by the operating system or a secure library.
Implement strong authentication and authorization mechanisms to mitigate the impact of compromised session IDs or tokens.
Regularly audit and update all software dependencies, including Perl modules.