CVE-2025-0577: glibc Insufficient Entropy Vulnerability

CVE-2025-0577 Overview

An insufficient entropy vulnerability was discovered in glibc affecting the getrandom and arc4random family of functions. These cryptographic random number generation functions may return predictable randomness when called after a fork() operation that occurs concurrently with a call to any of these functions. This race condition can lead to predictable random values being generated across forked processes, potentially compromising cryptographic operations that rely on these functions for secure random number generation.

Critical Impact

Applications using getrandom() or arc4random() for cryptographic operations may generate predictable random values after fork, potentially compromising session tokens, encryption keys, and other security-sensitive operations.

Affected Products

• GNU C Library (glibc) - versions with getrandom() and arc4random() implementations
• Linux distributions using affected glibc versions
• Applications relying on glibc's random number generation functions in multi-process environments

Discovery Timeline

• 2026-02-18 - CVE-2025-0577 published to NVD
• 2026-02-19 - Last updated in NVD database

Technical Details for CVE-2025-0577

Vulnerability Analysis

This vulnerability falls under CWE-331 (Insufficient Entropy), a cryptographic weakness where random number generators fail to produce values with adequate unpredictability. The core issue manifests during a specific race condition scenario: when a process calls fork() while another thread is concurrently executing getrandom() or any of the arc4random family functions.

In Unix-like systems, fork() creates a child process by duplicating the parent's memory space. Random number generators typically maintain internal state that must be properly reseeded in child processes to ensure unique random sequences. When the fork occurs during an active random number generation call, the internal state may be improperly shared or copied, causing both parent and child processes to generate identical or predictable random sequences.

Root Cause

The root cause is a race condition in glibc's random number generation implementation where the internal entropy pool state is not properly isolated during concurrent fork() operations. When getrandom() or arc4random() is being executed at the moment of fork, the entropy state may be:

1. Partially updated in both processes with the same seed material
2. Duplicated before reseeding can occur in the child process
3. Left in an inconsistent state that produces predictable outputs

This timing-dependent behavior means the vulnerability may not manifest consistently, making it particularly dangerous as it could pass standard testing but fail under production load conditions.

Attack Vector

The vulnerability requires network-accessible attack surface with high complexity requirements. An attacker would need to:

1. Identify an application using glibc's getrandom() or arc4random() functions for security-critical operations
2. Trigger conditions that cause the application to fork while random number generation is in progress
3. Observe or predict the random values generated by either the parent or child process
4. Exploit the predictable randomness to compromise session tokens, encryption keys, nonces, or other cryptographic materials

The attack is most feasible against multi-process server applications that fork to handle incoming connections while using these random functions for security operations. Successful exploitation could lead to unauthorized information disclosure or integrity compromise of cryptographic operations.

Detection Methods for CVE-2025-0577

Indicators of Compromise

• Duplicate or similar random values observed across forked processes in application logs
• Session tokens or cryptographic nonces that appear correlated between different user sessions
• Unexpected authentication bypasses or session collisions in multi-process applications
• Anomalous patterns in cryptographic operations suggesting reduced entropy

Detection Strategies

• Audit applications for concurrent use of fork() with getrandom(), arc4random(), arc4random_buf(), or arc4random_uniform()
• Review glibc version deployed across systems and compare against vendor security advisories
• Monitor for unusual patterns in random value generation using application-level logging
• Implement runtime detection for entropy quality degradation in security-critical applications

Monitoring Recommendations

• Enable detailed logging for cryptographic operations in multi-process applications
• Monitor for duplicate or low-entropy values in security tokens and session identifiers
• Track glibc library versions across infrastructure using software inventory tools
• Set up alerts for known vulnerable glibc package versions using vulnerability scanning tools

How to Mitigate CVE-2025-0577

Immediate Actions Required

• Review the Red Hat CVE-2025-0577 Advisory for vendor-specific guidance and patch availability
• Identify all systems running potentially affected glibc versions
• Audit applications that use getrandom() or arc4random() functions in conjunction with fork()
• Consider implementing application-level reseeding after fork operations as a temporary mitigation

Patch Information

Refer to your distribution vendor's security advisory for patch availability. Red Hat has published tracking information in Bugzilla Report #2338871. Monitor your distribution's security channels for updated glibc packages that address this insufficient entropy vulnerability.

Workarounds

• Explicitly reseed random number generators in child processes immediately after fork() by calling getrandom() with fresh entropy before any security-critical operations
• Avoid calling getrandom() or arc4random() functions in code paths that may execute concurrently with fork() operations
• Use synchronization mechanisms to prevent concurrent fork and random number generation calls
• Consider alternative entropy sources such as reading directly from /dev/urandom with proper locking in fork-sensitive code paths
• Implement pthread_atfork() handlers to properly reinitialize random state in child processes

# Check installed glibc version
ldd --version

# List packages that depend on glibc for audit
rpm -q --whatrequires glibc 2>/dev/null || dpkg -S /lib/x86_64-linux-gnu/libc.so.6 2>/dev/null

# Monitor for glibc security updates (Red Hat/CentOS)
yum updateinfo list security glibc

# Monitor for glibc security updates (Debian/Ubuntu)
apt-get changelog libc6 | grep -i CVE