CVE-2020-8450: Squid-cache Buffer Overflow Vulnerability

CVE-2020-8450 Overview

CVE-2020-8450 is a buffer overflow vulnerability discovered in Squid proxy server versions prior to 4.10. The flaw exists due to incorrect buffer management in Squid's reverse proxy functionality, allowing remote attackers to cause a buffer overflow by sending specially crafted requests to a vulnerable Squid instance configured as a reverse proxy.

This vulnerability affects organizations using Squid as a reverse proxy to front-end web applications, potentially exposing critical infrastructure to remote attacks without requiring authentication.

Critical Impact
Remote attackers can exploit incorrect buffer management in Squid reverse proxy configurations to cause buffer overflows, potentially leading to service disruption, information disclosure, or code execution on affected systems.

Affected Products

Squid-cache Squid (versions before 4.10)
Canonical Ubuntu Linux 16.04 LTS, 18.04 LTS, 19.10
openSUSE Leap 15.1
Fedora 30, 31
Debian Linux 9.0, 10.0

Discovery Timeline

February 4, 2020 - CVE-2020-8450 published to NVD
November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-8450

Vulnerability Analysis

This vulnerability stems from a buffer management error (CWE-131: Incorrect Calculation of Buffer Size) in Squid's reverse proxy implementation. When Squid operates as a reverse proxy, it handles incoming client requests and forwards them to backend servers. The vulnerability occurs during the processing of these requests, where improper buffer size calculations can lead to memory corruption.

The flaw is particularly concerning because it can be triggered remotely by any client that can reach the Squid proxy, without requiring any form of authentication. Squid's reverse proxy functionality is commonly deployed in enterprise environments to provide caching, load balancing, and security filtering for web applications, making this vulnerability relevant to many production deployments.

Root Cause

The root cause of CVE-2020-8450 is an incorrect buffer size calculation (CWE-131) in Squid's buffer management routines. When processing certain types of requests in reverse proxy mode, Squid fails to properly validate or calculate the required buffer size, allowing data to overflow the allocated memory region. This class of vulnerability can lead to memory corruption, denial of service, or potentially arbitrary code execution if an attacker can control the overflowed data.

Attack Vector

The attack can be executed remotely over the network by any client capable of sending HTTP requests to a Squid instance configured as a reverse proxy. The attacker does not need any special privileges or authentication to trigger the vulnerability.

An attack scenario involves sending specially crafted HTTP requests to a vulnerable Squid reverse proxy that trigger the buffer management flaw. When processed by Squid, these requests cause the buffer overflow condition. The impact includes potential denial of service through process crashes, information leakage from adjacent memory regions, and in severe cases, the possibility of code execution.

For technical details on the vulnerability mechanism and exploitation, refer to the Squid Security Advisory SQUID-2020_1.

Detection Methods for CVE-2020-8450

Indicators of Compromise

Unexpected Squid process crashes or restarts in reverse proxy configurations
Anomalous memory consumption patterns in Squid processes
Core dumps or segmentation faults in Squid logs
Unusual HTTP request patterns targeting the reverse proxy with malformed or oversized headers

Detection Strategies

Monitor Squid access logs for unusual request patterns, particularly requests with abnormally large headers or malformed content
Implement network-based intrusion detection rules to identify potential exploitation attempts targeting buffer overflow conditions
Deploy endpoint detection and response (EDR) solutions to identify memory corruption indicators in Squid processes
Use SentinelOne Singularity to detect and respond to behavioral anomalies associated with buffer overflow exploitation

Monitoring Recommendations

Enable verbose logging in Squid to capture detailed request information for forensic analysis
Configure system-level monitoring to alert on unexpected Squid service restarts or crashes
Implement memory usage monitoring for Squid processes to detect abnormal consumption patterns
Review Squid cache.log for error messages related to assertion failures or memory allocation issues

How to Mitigate CVE-2020-8450

Immediate Actions Required

Upgrade Squid to version 4.10 or later immediately on all systems operating in reverse proxy mode
If immediate patching is not possible, consider temporarily disabling reverse proxy functionality until updates can be applied
Review network access controls to limit exposure of Squid instances to trusted networks only
Implement Web Application Firewall (WAF) rules to filter potentially malicious requests

Patch Information

Squid has released patches addressing this vulnerability in version 4.10 and later. Multiple patch options are available for different Squid branches:

Linux distributions have also released security updates:

Workarounds

Restrict network access to Squid reverse proxy instances using firewall rules to trusted client networks only
Implement rate limiting and request size restrictions at the network perimeter
Deploy a WAF in front of Squid to inspect and filter potentially malicious HTTP requests
Consider disabling reverse proxy functionality temporarily if the risk is deemed unacceptable and patching cannot be performed immediately

bash

# Example: Restrict Squid access using iptables
# Allow only trusted networks to access Squid reverse proxy
iptables -A INPUT -p tcp --dport 3128 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 3128 -j DROP

# Example: Configure Squid request size limits in squid.conf
# Limit maximum request header size
request_header_max_size 64 KB