CVE-2020-11984: Apache HTTP Server RCE Vulnerability

CVE-2020-11984 Overview

CVE-2020-11984 is a buffer overflow vulnerability in Apache HTTP Server versions 2.4.32 through 2.4.44, specifically affecting the mod_proxy_uwsgi module. This vulnerability enables information disclosure and potentially allows remote code execution (RCE). The flaw exists in how the module handles specially crafted requests when proxying to a uWSGI backend, allowing attackers to overflow a buffer and potentially take complete control of affected systems.

Critical Impact

This vulnerability allows unauthenticated remote attackers to potentially achieve remote code execution or extract sensitive information from Apache HTTP Server instances using mod_proxy_uwsgi, representing a severe threat to web infrastructure security.

Affected Products

• Apache HTTP Server 2.4.32 to 2.4.44
• NetApp Clustered Data ONTAP
• Canonical Ubuntu Linux 16.04 LTS, 18.04 LTS, 20.04 LTS
• Debian Linux 9.0 and 10.0
• Fedora 31 and 32
• openSUSE Leap 15.1 and 15.2
• Oracle Communications Element Manager
• Oracle Communications Session Report Manager
• Oracle Communications Session Route Manager
• Oracle Enterprise Manager Ops Center 12.4.0.0
• Oracle Hyperion Infrastructure Technology 11.1.2.4
• Oracle Instantis EnterpriseTrack 17.1, 17.2, 17.3
• Oracle ZFS Storage Appliance Kit 8.8

Discovery Timeline

• August 7, 2020 - CVE-2020-11984 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-11984

Vulnerability Analysis

This vulnerability resides in the mod_proxy_uwsgi module of Apache HTTP Server, which provides proxy functionality for uWSGI application servers. The root issue is a classic buffer overflow (CWE-120) that occurs when the module improperly handles request data during the proxy operation.

When Apache HTTP Server is configured to proxy requests to a uWSGI backend using mod_proxy_uwsgi, malformed or oversized request data can overflow internal buffers. This memory corruption can lead to two primary exploitation scenarios: information disclosure, where an attacker can read memory contents beyond intended boundaries, and remote code execution, where careful manipulation of overflowed data can hijack program execution flow.

The vulnerability requires no authentication and can be exploited remotely over the network, making it particularly dangerous for internet-facing Apache installations using uWSGI proxying. Given the widespread deployment of Apache HTTP Server and the popularity of Python web applications using uWSGI, this vulnerability has broad potential impact.

Root Cause

The vulnerability stems from improper bounds checking when processing request data in the mod_proxy_uwsgi module (CWE-120: Buffer Copy without Checking Size of Input). The module fails to properly validate the size of incoming request data before copying it into a fixed-size buffer, allowing attackers to write beyond allocated memory boundaries.

Attack Vector

An attacker can exploit this vulnerability by sending specially crafted HTTP requests to an Apache HTTP Server configured with mod_proxy_uwsgi enabled. The attack is network-based and requires no user interaction or authentication. The attacker crafts requests with oversized or malformed data designed to overflow the vulnerable buffer in the proxy module. Upon successful exploitation, the attacker may leak sensitive memory contents or achieve arbitrary code execution with the privileges of the Apache HTTP Server process.

The exploitation mechanism involves manipulating the uWSGI protocol headers or request body in a way that causes the buffer overflow when Apache processes and forwards the request to the backend uWSGI server. For detailed technical analysis, refer to the Packet Storm Exploit Analysis.

Detection Methods for CVE-2020-11984

Indicators of Compromise

• Unexpected crashes or segmentation faults in Apache HTTP Server processes, particularly httpd worker processes
• Abnormal memory consumption patterns in Apache processes handling proxied requests
• Suspicious HTTP requests with unusually large headers or body content targeting uWSGI proxy endpoints
• Evidence of memory corruption or unexpected data in Apache error logs

Detection Strategies

• Monitor Apache error logs for segmentation faults, memory allocation errors, or unexpected process terminations
• Implement web application firewall (WAF) rules to detect and block oversized or malformed HTTP requests targeting proxy endpoints
• Use intrusion detection systems (IDS) to identify patterns consistent with buffer overflow exploitation attempts
• Deploy SentinelOne Singularity platform for behavioral detection of memory corruption exploitation and anomalous process behavior

Monitoring Recommendations

• Enable detailed Apache logging including request headers and sizes for forensic analysis
• Monitor system-level metrics for Apache processes including memory usage, CPU spikes, and unexpected process restarts
• Implement network traffic analysis to detect unusual patterns in traffic destined for uWSGI proxy configurations
• Configure alerting for Apache process crashes or restarts that may indicate exploitation attempts

How to Mitigate CVE-2020-11984

Immediate Actions Required

• Upgrade Apache HTTP Server to version 2.4.45 or later, which contains the fix for this vulnerability
• If immediate patching is not possible, disable mod_proxy_uwsgi if it is not required for operations
• Implement network segmentation to limit exposure of vulnerable Apache instances
• Deploy a web application firewall (WAF) to filter potentially malicious requests

Patch Information

Apache Software Foundation has released Apache HTTP Server version 2.4.46 which addresses this vulnerability. Organizations should update to version 2.4.46 or later to remediate CVE-2020-11984. Patches are also available through various Linux distribution channels including Ubuntu, Debian, Fedora, and openSUSE. Refer to the Apache HTTP Server Vulnerabilities page for official patch information. Additional vendor-specific patches are available from Oracle, NetApp, and Gentoo.

Workarounds

• Disable mod_proxy_uwsgi module if uWSGI proxying functionality is not required by running a2dismod proxy_uwsgi
• Implement strict input validation at the network perimeter using a WAF or reverse proxy that can filter oversized requests
• Restrict access to uWSGI proxy endpoints to trusted networks only using Apache access controls or firewall rules
• Consider using alternative proxy modules such as mod_proxy_http with a uWSGI HTTP connector as a temporary measure

# Disable mod_proxy_uwsgi on Debian/Ubuntu systems
sudo a2dismod proxy_uwsgi
sudo systemctl restart apache2

# Verify module is disabled
apache2ctl -M | grep uwsgi