CVE-2020-1934: Apache HTTP Server Memory Issue Vulnerability

CVE-2020-1934 Overview

CVE-2020-1934 is an uninitialized memory use vulnerability affecting Apache HTTP Server versions 2.4.0 through 2.4.41. The vulnerability exists within the mod_proxy_ftp module, which may use uninitialized memory when proxying requests to a malicious FTP server. This flaw could allow an attacker controlling a malicious FTP backend server to potentially leak sensitive information from the Apache HTTP Server's memory.

Critical Impact

Organizations using Apache HTTP Server with mod_proxy_ftp enabled to proxy FTP connections are at risk of information disclosure. An attacker operating a malicious FTP server could potentially extract sensitive data from uninitialized memory regions.

Affected Products

• Apache HTTP Server versions 2.4.0 through 2.4.41
• Fedora 31 and 32
• Debian Linux 9.0 and 10.0
• Canonical Ubuntu Linux 16.04 ESM, 18.04 LTS, and 20.04 LTS
• openSUSE Leap 15.1
• Oracle Communications Element Manager 8.1.1, 8.2.0, 8.2.1
• Oracle Communications Session Report Manager 8.1.1, 8.2.0, 8.2.1
• Oracle Communications Session Route Manager 8.1.1, 8.2.0, 8.2.1
• Oracle Enterprise Manager Ops Center 12.4.0.0
• Oracle Instantis EnterpriseTrack
• Oracle ZFS Storage Appliance Kit 8.8

Discovery Timeline

• April 1, 2020 - CVE-2020-1934 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-1934

Vulnerability Analysis

The vulnerability resides in the mod_proxy_ftp module of Apache HTTP Server, which provides FTP proxy functionality. When the module processes responses from a backend FTP server, it fails to properly initialize certain memory regions before use. This uninitialized memory use (CWE-908) creates a scenario where data from previous operations or other memory contents may be inadvertently exposed.

The attack requires an adversary to control or compromise an FTP server that the Apache HTTP Server is configured to proxy. When the vulnerable Apache server connects to this malicious FTP backend, the attacker can craft responses that trigger the uninitialized memory condition, potentially leaking sensitive information that was previously stored in those memory regions.

The vulnerability is exploitable over the network without requiring authentication or user interaction, making it accessible to remote attackers who can position themselves as a backend FTP server.

Root Cause

The root cause of CVE-2020-1934 is the failure to properly initialize memory buffers in the mod_proxy_ftp module before they are used to process FTP server responses. When memory is allocated but not initialized, it may contain residual data from previous allocations. The module's code path that handles certain FTP protocol interactions does not zero out or otherwise initialize these buffers, leading to the potential for information leakage when the contents of this uninitialized memory are processed or transmitted.

Attack Vector

The attack vector for this vulnerability involves a network-based attack where the attacker must either control a malicious FTP server or compromise an existing FTP backend that the vulnerable Apache HTTP Server is configured to proxy. The attack flow is as follows:

1. The attacker sets up or compromises an FTP server that is configured as a proxy backend for the target Apache HTTP Server
2. A client makes a request through the Apache proxy that results in a connection to the attacker-controlled FTP server
3. The attacker crafts specific FTP responses designed to trigger the uninitialized memory condition
4. The Apache server processes the response using uninitialized memory, potentially exposing sensitive data
5. The attacker receives the leaked memory contents through the FTP protocol exchange

The vulnerability requires specific configuration where mod_proxy_ftp is enabled and configured to proxy to FTP backends. Organizations that do not use FTP proxying functionality are not affected by this vulnerability.

Detection Methods for CVE-2020-1934

Indicators of Compromise

• Unexpected or anomalous FTP proxy requests to unknown or suspicious FTP server destinations
• Unusual memory patterns or error messages in Apache HTTP Server logs related to mod_proxy_ftp
• Network traffic showing FTP connections to untrusted or recently modified backend server addresses
• Apache error logs containing segmentation faults or memory-related errors during FTP proxy operations

Detection Strategies

• Monitor Apache HTTP Server configurations for mod_proxy_ftp usage and validate all configured FTP backend servers are trusted
• Implement network monitoring to detect FTP traffic patterns and identify connections to unauthorized FTP servers
• Deploy endpoint detection and response (EDR) solutions like SentinelOne to monitor Apache process behavior for memory anomalies
• Review Apache access and error logs for unusual FTP proxy activity or memory-related error conditions

Monitoring Recommendations

• Enable verbose logging for the mod_proxy_ftp module to capture detailed proxy transaction information
• Implement network segmentation monitoring to track FTP traffic flows from web server segments
• Configure alerting for any modifications to Apache proxy configuration files
• Use memory analysis tools to periodically audit Apache HTTP Server processes for memory handling issues

How to Mitigate CVE-2020-1934

Immediate Actions Required

• Upgrade Apache HTTP Server to version 2.4.42 or later, which contains the fix for this vulnerability
• If immediate patching is not possible, disable the mod_proxy_ftp module until the update can be applied
• Audit all FTP backend server configurations to ensure only trusted servers are configured as proxy destinations
• Implement network access controls to restrict which FTP servers the Apache HTTP Server can connect to

Patch Information

Apache has released a patched version addressing this vulnerability. Organizations should upgrade to Apache HTTP Server version 2.4.42 or later. The official security advisory is available at the Apache HTTP Server Security Vulnerabilities page.

For Linux distributions:

• Ubuntu: Security updates available via USN-4458-1
• Debian: Security updates available via DSA-4757
• Fedora: Updates available through the standard package management system
• Oracle Products: Refer to the Oracle Critical Patch Update July 2020

Workarounds

• Disable mod_proxy_ftp by commenting out or removing the LoadModule proxy_ftp_module directive in the Apache configuration if FTP proxying is not required
• Implement strict access control lists (ACLs) to limit which backend FTP servers can be accessed through the proxy
• Use a Web Application Firewall (WAF) to filter and monitor proxy requests to FTP destinations
• Deploy network segmentation to isolate the Apache HTTP Server from untrusted FTP server networks

# Disable mod_proxy_ftp in Apache configuration
# Edit httpd.conf or apache2.conf and comment out or remove:
# LoadModule proxy_ftp_module modules/mod_proxy_ftp.so

# On Debian/Ubuntu systems, disable the module:
sudo a2dismod proxy_ftp
sudo systemctl restart apache2

# On RHEL/CentOS systems, comment out the LoadModule line:
sudo sed -i 's/^LoadModule proxy_ftp_module/#LoadModule proxy_ftp_module/' /etc/httpd/conf.modules.d/00-proxy.conf
sudo systemctl restart httpd