CVE-2025-7394: WolfSSL Information Disclosure Vulnerability

CVE-2025-7394 Overview

A vulnerability exists in wolfSSL's OpenSSL compatibility layer where the RAND_poll() function does not behave as expected, leading to potentially predictable values returned from RAND_bytes() after fork() is called. This can result in weak or predictable random numbers generated in applications that both use RAND_bytes() and perform fork() operations.

Critical Impact

Applications using wolfSSL's OpenSSL compatibility layer may generate predictable cryptographic random numbers after fork() operations, potentially compromising cryptographic security in session keys, nonces, and other security-critical random values.

Affected Products

• wolfSSL wolfssl (all versions prior to 5.8.2)

Discovery Timeline

• July 17, 2025 - wolfSSL releases version 5.8.2 with security patch
• July 18, 2025 - CVE-2025-7394 published to NVD
• December 3, 2025 - Last updated in NVD database

Technical Details for CVE-2025-7394

Vulnerability Analysis

This vulnerability represents an insecure random number generation flaw in wolfSSL's OpenSSL compatibility layer implementation. The core issue stems from the RAND_poll() function not properly reseeding the random number generator after a fork() system call. When a process forks, both the parent and child processes share the same internal state of the pseudo-random number generator (PRNG). Without proper reseeding, both processes will generate identical sequences of "random" numbers, fundamentally undermining cryptographic security guarantees.

The vulnerability specifically affects the Hash-DRBG (Deterministic Random Bit Generator) used by wolfSSL when applications explicitly call RAND_bytes() after a fork() operation. While this does not affect internal TLS operations within wolfSSL, any application-level code relying on RAND_bytes() for cryptographic operations such as key generation, nonce creation, or IV generation could be severely impacted. The network attack vector indicates that affected applications exposed to network traffic could have their cryptographic protections weakened remotely.

Root Cause

The root cause is a failure in the OpenSSL compatibility layer's RAND_poll() implementation to properly detect and handle process forking scenarios. When fork() is called, the child process inherits the parent's PRNG state without triggering a reseed operation. Although OpenSSL's documentation explicitly warns that RAND_bytes() is not safe for use with fork() without first calling RAND_poll(), wolfSSL's implementation did not enforce this behavior or provide automatic reseeding upon detecting execution in a new process context.

Attack Vector

The vulnerability is exploitable over the network with high attack complexity. An attacker would need to:

1. Target an application using wolfSSL's OpenSSL compatibility layer
2. Wait for or trigger conditions where the application calls fork() followed by RAND_bytes()
3. Predict or influence the random values generated due to the shared PRNG state between parent and child processes
4. Leverage predictable random numbers to compromise cryptographic operations

The attack scenario typically involves applications that fork worker processes or daemon services that generate cryptographic material. If an attacker can observe or predict the output of one process, they may be able to deduce the random values used by the forked process, potentially compromising session keys, authentication tokens, or other security-critical values.

Detection Methods for CVE-2025-7394

Indicators of Compromise

• Applications generating identical cryptographic values across forked processes
• Unexpected collisions in session identifiers or cryptographic nonces
• Anomalous patterns in TLS session tickets or random values in network traffic from forked services
• Evidence of cryptographic material reuse in security logs

Detection Strategies

• Audit application code for patterns where RAND_bytes() is called after fork() without intervening RAND_poll() calls
• Implement runtime monitoring to detect identical random value sequences across process boundaries
• Use static analysis tools to identify vulnerable code patterns in applications linked against wolfSSL
• Review wolfSSL version deployed across your infrastructure to identify instances running versions prior to 5.8.2

Monitoring Recommendations

• Monitor cryptographic entropy sources and PRNG seeding events in security-sensitive applications
• Implement logging for fork() operations in applications using wolfSSL's OpenSSL compatibility layer
• Set up alerts for wolfSSL version mismatches in your software inventory management systems
• Track security advisories from wolfSSL for related updates and guidance

How to Mitigate CVE-2025-7394

Immediate Actions Required

• Update wolfSSL to version 5.8.2 or later immediately
• Audit all applications using wolfSSL's OpenSSL compatibility layer for fork() + RAND_bytes() patterns
• As a temporary measure, ensure RAND_poll() is explicitly called after every fork() operation before using RAND_bytes()
• Regenerate any cryptographic keys or secrets that may have been generated by vulnerable code paths

Patch Information

wolfSSL has released version 5.8.2 which addresses this vulnerability. The fix implements automatic reseeding of the Hash-DRBG when the library detects that it is running in a new process after a fork() operation. This makes RAND_bytes() behave similarly to OpenSSL's implementation after a fork() call, even without an explicit RAND_poll() invocation. For detailed release information, see the wolfSSL Release 5.8.2 ChangeLog.

Workarounds

• If immediate upgrade is not possible, modify application code to call RAND_poll() immediately after every fork() operation
• Consider implementing a custom entropy injection mechanism after fork() operations
• For critical systems, temporarily disable forking patterns that use RAND_bytes() until the patch can be applied
• Implement application-level random value validation to detect potential duplicate values across processes

# Verify wolfSSL version to ensure patched release is installed
# Check installed wolfSSL version
wolfssl-version

# For systems using package managers, verify the installed version
# Debian/Ubuntu
dpkg -l | grep wolfssl

# RedHat/CentOS
rpm -qa | grep wolfssl

# Update to latest wolfSSL version 5.8.2 or later
# Build from source if using custom compilation
cd wolfssl-5.8.2
./configure --enable-opensslcoexist
make
sudo make install