CVE-2026-27784: NGINX Open Source DoS Vulnerability

CVE-2026-27784 Overview

CVE-2026-27784 is an Integer Overflow vulnerability affecting the 32-bit implementation of NGINX Open Source within the ngx_http_mp4_module module. This vulnerability allows an attacker to over-read or over-write NGINX worker memory through a specially crafted MP4 file, potentially resulting in worker process termination and denial of service conditions.

The vulnerability specifically impacts 32-bit NGINX Open Source deployments where the ngx_http_mp4_module module is compiled in and the mp4 directive is actively used in the configuration file. Exploitation requires an attacker to trigger processing of a malicious MP4 file through the vulnerable module.

Critical Impact

Successful exploitation can cause NGINX worker process termination through memory over-read or over-write conditions, leading to service disruption for applications relying on MP4 streaming functionality.

Affected Products

• NGINX Open Source (32-bit builds with ngx_http_mp4_module enabled)
• Systems using the mp4 directive in NGINX configuration
• Deployments serving MP4 content through NGINX streaming

Discovery Timeline

• 2026-03-24 - CVE-2026-27784 published to NVD
• 2026-03-24 - Last updated in NVD database

Technical Details for CVE-2026-27784

Vulnerability Analysis

This vulnerability is classified under CWE-190 (Integer Overflow or Wraparound), indicating that the ngx_http_mp4_module fails to properly validate integer boundaries when processing MP4 file structures. On 32-bit systems, this integer handling limitation becomes exploitable due to the constrained memory address space and integer size limitations inherent to 32-bit architectures.

The attack requires local access to trigger processing of a malicious MP4 file. While this limits the attack surface compared to remote exploitation scenarios, environments that accept user-uploaded media content for streaming could be vulnerable if those files are processed by the vulnerable module.

The impact includes potential confidentiality breach through memory over-read operations, integrity compromise through memory over-write capabilities, and availability impact through worker process termination.

Root Cause

The root cause is an integer overflow condition (CWE-190) in the ngx_http_mp4_module module's handling of MP4 file metadata. When parsing certain MP4 atom structures on 32-bit systems, the module performs arithmetic operations that can wrap around, leading to incorrect memory offset calculations. This causes subsequent memory operations to access unintended memory regions, resulting in either information disclosure (over-read) or memory corruption (over-write).

Attack Vector

The attack vector requires local access with low privileges and no user interaction. An attacker must be able to place or upload a specially crafted MP4 file that will be processed by NGINX's ngx_http_mp4_module. This could occur through:

1. Direct file system access to place malicious MP4 files in directories served by NGINX
2. Exploiting file upload functionality in web applications that store content in NGINX-served directories
3. Manipulating content delivery systems that use NGINX for MP4 streaming

The vulnerability mechanism involves crafting MP4 atom sizes or offsets that cause integer overflow during arithmetic operations within the module, leading to the calculation of invalid memory addresses for subsequent read or write operations.

Detection Methods for CVE-2026-27784

Indicators of Compromise

• Unexpected NGINX worker process crashes or restarts when serving MP4 content
• Segmentation fault or memory access violation errors in NGINX error logs
• Presence of unusually structured or malformed MP4 files in media directories
• Core dump files indicating memory corruption in ngx_http_mp4_module related functions

Detection Strategies

• Monitor NGINX error logs for segmentation faults and memory-related errors during MP4 processing
• Implement file integrity monitoring on directories containing MP4 content served by NGINX
• Deploy application-layer inspection for MP4 files with anomalous atom structures or sizes
• Use endpoint detection solutions to identify suspicious MP4 file characteristics

Monitoring Recommendations

• Configure alerting for NGINX worker process termination events
• Enable core dump analysis for NGINX processes to identify exploitation attempts
• Monitor system logs for unusual patterns of process restarts associated with media requests
• Implement logging for all MP4 file access events to establish baseline behavior

How to Mitigate CVE-2026-27784

Immediate Actions Required

• Identify all 32-bit NGINX Open Source deployments using ngx_http_mp4_module
• Audit NGINX configurations for use of the mp4 directive
• Consider migrating to 64-bit NGINX builds where possible to eliminate this vulnerability class
• Restrict access to MP4 upload and storage directories
• Implement input validation for any user-uploaded media content

Patch Information

Consult the F5 Security Article K000160364 for official patch information and updated NGINX versions that address this vulnerability. Organizations should prioritize applying vendor-provided patches as they become available.

Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated and may remain vulnerable.

Workarounds

• Disable the ngx_http_mp4_module if MP4 streaming functionality is not required
• Remove mp4 directives from NGINX configuration files to prevent vulnerable code paths
• Migrate to 64-bit NGINX deployments which are not affected by this vulnerability
• Implement strict access controls limiting who can upload or place MP4 files on the server
• Deploy a reverse proxy or WAF to inspect and validate MP4 files before they reach NGINX

# Configuration example - Disable mp4 module processing
# Comment out or remove mp4 directives in nginx.conf

# Before (vulnerable):
# location /videos/ {
#     mp4;
#     mp4_buffer_size 1m;
#     mp4_max_buffer_size 5m;
# }

# After (mitigated - remove mp4 processing):
location /videos/ {
    # mp4 directive removed to mitigate CVE-2026-27784
    # Serve files statically without mp4 module processing
    root /var/www/media;
}