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The CVE-2025-XXXXX vulnerability exists within the `EncryptionUtilityServiceImpl` class of the Sakai platform. This service is responsible for generating a server-side secret key (serverSecretKey) used for AES-256 encryption of data. The flaw occurs because the key generation relies on org.apache.commons.lang3.RandomStringUtils.random(32), which internally uses `java.util.Random` as its pseudorandom number generator (PRNG). `java.util.Random` is a linear congruential generator (LCG) designed for non-cryptographic purposes. It generates a sequence of numbers that appears random but is entirely deterministic based on a single 48-bit seed value. If an attacker can approximate the system time when the seed was generated, the possible seed space is drastically reduced from a cryptographic 256-bit key to a much smaller, feasible brute-force space. By obtaining encrypted data and predicting the PRNG’s output sequence, an attacker could reconstruct the `serverSecretKey` and decrypt any sensitive information protected by this weak key.
Platform: Sakai
Version: <= 23.3
Vulnerability : Predictable PRNG
Severity: Low
date: 2025-10-22
Prediction: 2025-11-19
What Undercode Say:
Using a known seed to replicate java.util.Random output
java -cp .:commons-lang3-3.12.0.jar ReplicateRandom 12345
Sample Java code to demonstrate predictable key generation
import org.apache.commons.lang3.RandomStringUtils;
import java.util.Random;
public class WeakKeyGen {
public static void main(String[] args) {
// This mimics the vulnerable code
Random predictableRandom = new Random(12345L); // Using a fixed seed
String weakKey = RandomStringUtils.random(32, 0, 0, true, true, null, predictableRandom);
System.out.println("Generated Key: " + weakKey);
}
}
How Exploit:
An attacker exports or gains access to ciphertexts encrypted by the vulnerable service. By approximating the server’s startup time or another event that seeded the PRNG, the attacker brute-forces the possible seed values. For each candidate seed, they re-instantiate java.util.Random, regenerate the potential serverSecretKey, and attempt to decrypt the ciphertext. A successful decryption reveals the plaintext and confirms the correct key.
Protection from this CVE
Upgrade to Sakai versions 23.5, 25.0, or later which contain the patch for SAK-49866. The patch replaces the use of `java.util.Random` with a cryptographically secure PRNG (CSPRNG) like `java.security.SecureRandom` for generating the serverSecretKey.
Impact:
The confidentiality of data encrypted by the `EncryptionUtilityServiceImpl` is compromised. Attackers who can obtain the ciphertext and approximate the PRNG seed can decrypt sensitive information stored or exported from the system, such as user data or configuration settings.
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Sources:
Reported By: github.com
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