CVE-2025-55131: Node.js Information Disclosure Vulnerability

CVE-2025-55131 Overview

A flaw in Node.js's buffer allocation logic can expose uninitialized memory when allocations are interrupted, specifically when using the vm module with the timeout option. Under specific timing conditions, buffers allocated with Buffer.alloc and other TypedArray instances like Uint8Array may contain leftover data from previous operations, allowing in-process secrets like tokens or passwords to leak or causing data corruption. While exploitation typically requires precise timing or in-process code execution, it can become remotely exploitable when untrusted input influences workload and timeouts, leading to potential confidentiality and integrity impact.

Critical Impact

This vulnerability can expose sensitive in-memory data including authentication tokens, passwords, and other secrets when buffer allocations are interrupted during vm module execution with timeout options.

Affected Products

• Node.js (versions utilizing the vm module with timeout functionality)
• Applications using Buffer.alloc in conjunction with vm module timeouts
• Services processing untrusted input that influences workload timing

Discovery Timeline

• 2026-01-20 - CVE CVE-2025-55131 published to NVD
• 2026-01-20 - Last updated in NVD database

Technical Details for CVE-2025-55131

Vulnerability Analysis

This vulnerability represents an Uninitialized Memory Use flaw in Node.js's buffer allocation mechanism. The issue arises when buffer allocations within the vm module are interrupted due to timeout conditions. Under normal circumstances, Buffer.alloc is designed to zero-initialize memory before returning it to the caller, ensuring that no residual data from previous operations is exposed.

However, when execution within the vm module is terminated due to a timeout, the buffer allocation process may be interrupted at a point where memory has been allocated but not yet fully initialized. This creates a race condition where the allocated buffer may still contain data from previous memory operations, including potentially sensitive information such as authentication tokens, session identifiers, passwords, or cryptographic keys that were previously stored in that memory region.

The attack vector is network-based but requires high complexity to exploit successfully. An attacker would need to either have low-privilege access to execute code within the application or be able to influence the timing of operations through untrusted input. When untrusted input controls workload parameters and timeout values, this vulnerability can potentially be exploited remotely.

Root Cause

The root cause lies in the buffer allocation logic not properly handling interruption scenarios when the vm module's timeout mechanism triggers script termination. The memory allocation and initialization are not atomic operations, allowing a window where allocated but uninitialized memory can be returned to the caller. This violates the expected behavior of Buffer.alloc which should always return zero-initialized memory, and similarly affects TypedArray instances like Uint8Array.

Attack Vector

The attack vector involves manipulating the timing of buffer allocations within vm module contexts. An attacker with the ability to influence workload timing—either through direct code execution or by controlling input that affects timeout conditions—can attempt to trigger the vulnerability. The exploitation path typically involves:

1. Creating conditions where buffer allocations occur within vm.runInContext() or similar functions with timeout options enabled
2. Triggering timeout conditions at precise moments during buffer initialization
3. Reading the resulting buffer contents which may contain uninitialized memory from previous operations
4. Extracting sensitive data that resided in the leaked memory regions

The vulnerability is particularly concerning in multi-tenant environments or applications that process untrusted user input within sandboxed vm contexts, as the leaked memory could contain data from other tenants or privileged operations.

Detection Methods for CVE-2025-55131

Indicators of Compromise

• Unusual patterns of vm module usage with aggressive timeout configurations
• Memory access patterns showing reads of buffer data immediately after allocation failures or timeout events
• Application logs showing unexpected timeout terminations during buffer-intensive operations
• Anomalous data appearing in application outputs that resembles fragments of authentication tokens or credentials

Detection Strategies

• Monitor for applications using the vm module with timeout options in production environments
• Implement runtime analysis to detect buffer allocations that may not be properly initialized
• Review application code for patterns where untrusted input influences timeout values or workload parameters
• Deploy memory sanitizers in development and staging environments to identify uninitialized memory reads

Monitoring Recommendations

• Enable verbose logging for vm module operations and timeout events
• Implement application-level monitoring for buffer allocation patterns around timeout boundaries
• Set up alerts for unusual memory access patterns that may indicate exploitation attempts
• Monitor for data exfiltration attempts that could leverage leaked memory contents

How to Mitigate CVE-2025-55131

Immediate Actions Required

• Review all application code that uses the vm module with timeout options
• Assess whether untrusted input can influence timeout values or workload timing
• Consider temporarily disabling or restricting the use of vm module timeouts in sensitive contexts
• Update Node.js to the latest patched version when available

Patch Information

Node.js has addressed this vulnerability in security releases. Refer to the Node.js December 2025 Security Blog for detailed patch information and affected version guidance. Organizations should prioritize updating to patched versions as soon as they are available for their deployment environments.

Workarounds

• Avoid using the vm module with timeout options when processing untrusted input
• Implement explicit memory zeroing after buffer allocation in security-sensitive contexts
• Add validation layers to prevent untrusted input from influencing timeout configurations
• Consider using alternative sandboxing mechanisms that do not exhibit this memory exposure behavior
• Implement memory isolation between tenant operations in multi-tenant environments

# Example: Check Node.js version and update
node --version
# Update to the latest patched version from your package manager
# For nvm users:
nvm install --lts
nvm use --lts