CVE-2018-25107: Perl's Crypt::Random::Source Package's Security Vulnerability - Falling Back to the Insecure Built-in Rand() Function

In this post, we will delve into a particular security vulnerability found in Perl's Crypt::Random::Source package with versions before .13. This issue, identified as CVE-2018-25107, stems from the package's fallback mechanism that relies on the built-in rand() function. This implementation creates weaknesses because the rand() function is not a secure source of random bits. We will discuss the vulnerability in more depth, share insights on how to exploit it, and provide the necessary code snippets and fixes to help better understand and handle this issue.

The Vulnerability

When cryptographic systems require random numbers to ensure security and proper functioning, it is crucial to have a dependable and secure source of random bits. Failure to use a secure source may expose these systems to security threats and compromise their integrity.

Perl's Crypt::Random::Source package is used to get random bits from various sources. However, in versions before .13, there is a vulnerability due to its fallback mechanism, which relies on the built-in rand() function. The rand() function is found to be insecure and not a trustworthy source of random numbers, creating a potential opening for attackers to take advantage of.

Exploiting the Vulnerability

An attacker can exploit this vulnerability by predicting or controlling the output of the rand() function, thereby weakening the cryptographic processes that depend on secure random numbers. This may lead to compromised security of encrypted data and the possibility of unauthorized access to sensitive information.

Code Snippet

Here's a piece of code that demonstrates how rand() might be used as a fallback source of randomness in an insecure manner:

use Crypt::Random::Source;

my $source = Crypt::Random::Source->new;

my $random_number;
if ($source) {
    $random_number = $source->get();
} else {
    $random_number = rand();
}

In this example, the Crypt::Random::Source object is created, and if a secure random source is unavailable, the code falls back to using the insecure rand() function.

Original References

1. Original vulnerability details and report: CVE-2018-25107
2. More information on Perl's Crypt::Random::Source package: Crypt::Random::Source

Fixing the Vulnerability

To fix this vulnerability, users of Crypt::Random::Source should upgrade to version .13 or later, which no longer falls back to the insecure rand() function. Alternatively, users should ensure that secure random number sources are always available and never fallback to using the insecure built-in rand() function.

To upgrade the Crypt::Random::Source package, you can use the following command

cpanm Crypt::Random::Source@.13

Conclusion

The CVE-2018-25107 vulnerability in Perl's Crypt::Random::Source package is a reminder of the importance of using secure sources for random bits in cryptographic systems. By understanding this issue and taking the necessary steps to fix or prevent it, developers and users can alleviate potential security threats and maintain the integrity of their systems.

Timeline

Published on: 12/29/2024 07:15:05 UTC
Last modified on: 12/31/2024 19:15:07 UTC