CVE-2020-8265: Node.js Use-After-Free Vulnerability

CVE-2020-8265 Overview

CVE-2020-8265 is a use-after-free vulnerability in Node.js's TLS implementation that affects multiple versions of the runtime. The flaw exists in the handling of WriteWrap objects when writing to TLS-enabled sockets, where improper memory management can lead to memory corruption. This vulnerability allows remote attackers to potentially cause a Denial of Service condition or achieve other exploitation outcomes through network-accessible TLS connections.

Critical Impact

This use-after-free vulnerability in Node.js TLS implementation can lead to memory corruption, enabling Denial of Service attacks and potentially arbitrary code execution on affected servers handling TLS connections.

Affected Products

• Node.js versions before 10.23.1 (LTS)
• Node.js versions before 12.20.1 (LTS)
• Node.js versions before 14.15.4 (LTS)
• Node.js versions before 15.5.1
• Debian Linux 10.0
• Fedora 32 and 33
• Oracle GraalVM Enterprise 19.3.4 and 20.3.0
• Siemens SINEC Infrastructure Network Services

Discovery Timeline

• January 6, 2021 - CVE-2020-8265 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-8265

Vulnerability Analysis

This vulnerability (CWE-416: Use After Free) resides in Node.js's TLS layer, specifically in the interaction between the node::StreamBase::Write function and node::TLSWrap::DoWrite method. When an application writes data to a TLS-enabled socket, the StreamBase::Write function allocates a fresh WriteWrap object and passes it as the first argument to TLSWrap::DoWrite.

The vulnerability manifests when the DoWrite method does not return an error—in this scenario, the WriteWrap object pointer is returned to the caller as part of a StreamWriteResult structure. However, under certain conditions, this memory may have already been freed or reallocated, creating a classic use-after-free condition where subsequent operations reference invalid memory.

Root Cause

The root cause lies in improper memory lifecycle management of the WriteWrap object within the TLS write path. The object's lifetime is not properly synchronized between the caller (StreamBase::Write) and the callee (TLSWrap::DoWrite). When the DoWrite operation succeeds without error, the assumption that the WriteWrap object remains valid is violated under specific race conditions or operational sequences, leading to memory being accessed after deallocation.

Attack Vector

The attack vector is network-based, requiring no user interaction or privileges. An attacker can exploit this vulnerability by:

1. Establishing a TLS connection to a vulnerable Node.js server
2. Crafting TLS write operations that trigger the specific code path where the use-after-free occurs
3. Timing the exploitation to corrupt memory when the freed WriteWrap object is referenced

The exploitation requires high attack complexity due to the timing-sensitive nature of use-after-free conditions, but successful exploitation can result in complete compromise of confidentiality, integrity, and availability of the affected system.

The vulnerability mechanism involves memory corruption in the TLS write handling path. When node::StreamBase::Write invokes node::TLSWrap::DoWrite, the allocated WriteWrap object may be freed prematurely while a reference to it is still being used in the StreamWriteResult structure. Attackers targeting this vulnerability would need to trigger specific sequences of TLS write operations to manipulate memory state. For detailed technical analysis, refer to the HackerOne Report #988103 and the Node.js Security Release January 2021.

Detection Methods for CVE-2020-8265

Indicators of Compromise

• Unexpected Node.js process crashes or segmentation faults during TLS operations
• Memory corruption errors in Node.js application logs related to TLS socket writes
• Abnormal memory consumption patterns in Node.js processes handling TLS connections
• Core dumps indicating heap corruption in node::TLSWrap or StreamBase code paths

Detection Strategies

• Monitor Node.js process stability and crash frequency, particularly during high-volume TLS operations
• Implement application performance monitoring (APM) to detect anomalous TLS connection handling patterns
• Deploy memory debugging tools (e.g., AddressSanitizer) in staging environments to identify use-after-free conditions
• Use intrusion detection systems to identify unusual TLS handshake or data transfer patterns targeting Node.js endpoints

Monitoring Recommendations

• Enable verbose logging for TLS operations in Node.js applications to capture potential exploitation attempts
• Configure alerting for Node.js process restarts and crashes on production servers
• Monitor network traffic patterns for unusual TLS connection sequences to Node.js services
• Track memory utilization metrics for Node.js processes to identify potential memory corruption events

How to Mitigate CVE-2020-8265

Immediate Actions Required

• Upgrade Node.js to version 10.23.1, 12.20.1, 14.15.4, or 15.5.1 or later immediately
• Identify all Node.js installations in your environment, including those embedded in applications and containers
• Prioritize patching internet-facing Node.js services that handle TLS connections
• Review and update container base images that include vulnerable Node.js versions

Patch Information

Node.js has released security patches addressing this vulnerability across all affected release lines. Organizations should upgrade to the following minimum versions:

• Node.js 10.x LTS: Upgrade to 10.23.1 or later
• Node.js 12.x LTS: Upgrade to 12.20.1 or later
• Node.js 14.x LTS: Upgrade to 14.15.4 or later
• Node.js 15.x: Upgrade to 15.5.1 or later

For additional platform-specific guidance, refer to:

• Node.js Security Release January 2021
• Debian Security Advisory DSA-4826
• Oracle Critical Patch Update January 2021
• Siemens Security Advisory SSA-389290

Workarounds

• Implement network-level controls to limit TLS connection rates to Node.js services
• Deploy a TLS-terminating reverse proxy in front of vulnerable Node.js applications to reduce direct exposure
• Consider disabling TLS on affected Node.js applications and offloading TLS termination to infrastructure components where feasible
• Implement application-level rate limiting for TLS connection establishment

# Check current Node.js version
node --version

# Update Node.js using package manager (example for Debian/Ubuntu)
sudo apt update
sudo apt install nodejs

# Verify updated version meets minimum requirements
node --version
# Should be >= 10.23.1, 12.20.1, 14.15.4, or 15.5.1 depending on release line