CVE-2024-27983: Node.js HTTP/2 Race Condition Vulnerability

CVE-2024-27983 Overview

CVE-2024-27983 is a high-severity race condition vulnerability affecting Node.js HTTP/2 server implementations. An attacker can completely disrupt the availability of a Node.js HTTP/2 server by sending a small number of HTTP/2 frame packets. The vulnerability occurs when HTTP/2 CONTINUATION frames are sent to the server followed by an abrupt TCP connection closure, triggering the Http2Session destructor while header frames are still being processed. This creates a race condition that leaves data in nghttp2 memory after reset, ultimately causing a denial of service condition.

Critical Impact

This vulnerability allows unauthenticated remote attackers to completely crash Node.js HTTP/2 servers with minimal network traffic, causing significant service disruption.

Affected Products

• Node.js HTTP/2 server implementations
• Applications using nghttp2 library for HTTP/2 processing
• Fedora, Debian, and other Linux distributions with affected Node.js packages

Discovery Timeline

• 2024-04-03 - Vulnerability disclosed on Openwall OSS Security mailing list
• 2024-04-09 - CVE-2024-27983 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2024-27983

Vulnerability Analysis

This vulnerability exploits a race condition (CWE-362) in how Node.js HTTP/2 servers handle the Http2Session destructor during connection termination. The flaw lies in the asynchronous processing of HTTP/2 header frames, specifically when CONTINUATION frames are involved.

When a client sends HTTP/2 headers using CONTINUATION frames and then abruptly closes the TCP connection, the server's Http2Session destructor is triggered while header frames are still being processed and stored in memory. This timing-dependent behavior creates a race condition where data can remain in nghttp2 memory after the session reset, leading to resource exhaustion and server unavailability.

The attack is particularly dangerous because it requires only a small amount of network traffic to achieve a complete denial of service. The vulnerability can be exploited remotely without any authentication, and the attacker does not need any special privileges or user interaction.

Root Cause

The root cause is improper synchronization between the HTTP/2 header frame processing logic and the session cleanup mechanism in Node.js. When the TCP connection is abruptly terminated during header processing, the Http2Session destructor does not properly coordinate with the ongoing frame processing, creating a race condition. This results in memory being left in an inconsistent state within the nghttp2 library, causing the server to become unavailable.

Attack Vector

The attack leverages the network-accessible HTTP/2 protocol to exploit this race condition. An attacker initiates an HTTP/2 connection to the target server and sends a sequence of HTTP/2 frames containing headers with CONTINUATION frames. Before the server completes processing these frames, the attacker abruptly terminates the TCP connection. This timing-sensitive sequence triggers the race condition between header processing and session destruction.

The attack mechanism involves the following steps:

1. The attacker establishes an HTTP/2 connection to the vulnerable Node.js server
2. The attacker sends HTTP/2 header frames using CONTINUATION frames to extend the header block
3. Before the server finishes processing all header frames, the attacker abruptly closes the TCP connection
4. The sudden connection closure triggers the Http2Session destructor while frames are still being processed
5. The race condition causes data to remain in nghttp2 memory after reset, leading to server instability

For detailed technical analysis, refer to the HackerOne Report #2319584 and CERT Vulnerability Report #421644.

Detection Methods for CVE-2024-27983

Indicators of Compromise

• Unusual patterns of HTTP/2 connections with abrupt terminations
• Server logs showing Http2Session errors or destructor-related crashes
• Memory consumption anomalies in Node.js processes during HTTP/2 traffic
• Increased rate of incomplete HTTP/2 sessions with CONTINUATION frames

Detection Strategies

• Monitor HTTP/2 connection patterns for rapid connect/disconnect cycles
• Implement alerting on Node.js process crashes or restarts with HTTP/2-related stack traces
• Deploy network intrusion detection rules for malformed HTTP/2 CONTINUATION frame sequences
• Use application performance monitoring to detect sudden availability drops in HTTP/2 services

Monitoring Recommendations

• Enable detailed logging for HTTP/2 session lifecycle events including creation and destruction
• Monitor memory usage patterns of Node.js processes handling HTTP/2 traffic
• Set up health checks specifically targeting HTTP/2 endpoints
• Implement rate limiting alerts for suspicious connection patterns to HTTP/2 services

How to Mitigate CVE-2024-27983

Immediate Actions Required

• Update Node.js to the latest patched version immediately
• Review and apply security updates from your Linux distribution (Fedora, Debian, etc.)
• Consider temporarily disabling HTTP/2 support if updates cannot be applied immediately
• Implement rate limiting on HTTP/2 connections at the network edge

Patch Information

Security patches addressing CVE-2024-27983 have been released through multiple channels. Organizations should apply updates from their respective package managers:

• Fedora: Updates available via Fedora Package Announcements
• Debian: Updates available via Debian LTS Announcement
• NetApp Products: Refer to the NetApp Security Advisory

Workarounds

• Deploy a reverse proxy or load balancer that can filter or rate-limit HTTP/2 connections before they reach the Node.js server
• Implement connection timeouts to terminate long-running or suspicious HTTP/2 sessions
• If HTTP/2 is not required, configure the server to use HTTP/1.1 only until patches can be applied
• Use network-level controls to limit the rate of new HTTP/2 connections from individual IP addresses

# Example: Disable HTTP/2 in Node.js server configuration
# In your Node.js application, use HTTP/1.1 only as a temporary workaround
export NODE_OPTIONS="--http-server-default-timeout=30000"

# Or configure reverse proxy (nginx example) to handle HTTP/2 termination
# and proxy HTTP/1.1 to Node.js backend
# nginx.conf snippet:
# listen 443 ssl http2;
# proxy_http_version 1.1;