CVE-2023-50269 – Squid caching proxy versions 2.6 through 6.5 co... (How to Fix)

Q: What is the severity of CVE-2023-50269?

CVE-2023-50269 has a CVSS score of 8.6 (HIGH). Squid caching proxy versions 2.6 through 6.5 contain an uncontrolled recursion vulnerability in HTTP request parsing when the follow_x_forwarded_for feature is enabled. Remote attackers can cause denial of service by sending specially crafted X-Forwarded-For headers, potentially crashing the Squid service. This affects all systems running vulnerable Squid versions with the vulnerable configuration enabled.

📋 TL;DR

Squid caching proxy versions 2.6 through 6.5 contain an uncontrolled recursion vulnerability in HTTP request parsing when the follow_x_forwarded_for feature is enabled. Remote attackers can cause denial of service by sending specially crafted X-Forwarded-For headers, potentially crashing the Squid service. This affects all systems running vulnerable Squid versions with the vulnerable configuration enabled.

💻 Affected Systems

Products:

Squid caching proxy

Versions: 2.6 through 2.7.STABLE9, 3.1 through 5.9, 6.0.1 through 6.5

Operating Systems: All operating systems running Squid

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when follow_x_forwarded_for feature is configured and enabled. Default configurations may not be vulnerable.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete service outage where Squid crashes and becomes unavailable, disrupting all web proxy traffic for dependent systems and users.

🟠

Likely Case

Service degradation or temporary unavailability requiring manual restart of Squid processes, causing intermittent connectivity issues for users.

🟢

If Mitigated

Minimal impact with proper rate limiting, header size restrictions, and monitoring in place to detect and block attack attempts.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires sending HTTP requests with malicious X-Forwarded-For headers to vulnerable Squid instances.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 6.6

Vendor Advisory: https://github.com/squid-cache/squid/security/advisories/GHSA-wgq4-4cfg-c4x3

Restart Required: Yes

Instructions:

1. Upgrade to Squid version 6.6 or later. 2. Apply vendor patches for stable releases if upgrading is not possible. 3. Restart Squid service after patching.

🔧 Temporary Workarounds

Disable follow_x_forwarded_for

all

Disable the vulnerable feature if not required for functionality

Edit squid.conf and set 'follow_x_forwarded_for deny all' or remove related configurations

Limit header size

all

Configure maximum request header size to restrict malicious payloads

Add 'request_header_max_size 64 KB' to squid.conf (adjust size as needed)

🧯 If You Can't Patch

Implement network-level filtering to block or limit X-Forwarded-For headers exceeding reasonable size
Deploy WAF or reverse proxy in front of Squid to sanitize and validate incoming headers

🔍 How to Verify

Check if Vulnerable:

Check Squid version with 'squid -v' and verify if follow_x_forwarded_for is enabled in squid.conf

Check Version:

squid -v | head -1

Verify Fix Applied:

Confirm Squid version is 6.6 or later, or verify applied patches, then test with crafted X-Forwarded-For headers

📡 Detection & Monitoring

Log Indicators:

Multiple requests with unusually large X-Forwarded-For headers
Squid process crashes or restarts
High CPU/memory usage spikes

Network Indicators:

HTTP requests containing X-Forwarded-For headers exceeding normal size (e.g., >1KB)
Increased error responses from Squid

SIEM Query:

source="squid" AND ("X-Forwarded-For" AND content_length>1024) OR "segmentation fault" OR "crash"

📊 Metadata

CVE ID: CVE-2023-50269

CVSS v3 Score: 8.6 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

CWE: CWE-674

Published: December 14, 2023

Last Updated: November 21, 2024

🔗 References

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📋 TL;DR

💻 Affected Systems

📦 What is this software?

Squid by Squid Cache

Squid by Squid Cache

Squid by Squid Cache

Squid by Squid Cache

Squid by Squid Cache

Squid by Squid Cache

Squid by Squid Cache

Squid by Squid Cache

Squid by Squid Cache

Squid by Squid Cache

Squid by Squid Cache

Squid by Squid Cache

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⚠️ Risk & Real-World Impact

Worst Case

Likely Case

If Mitigated

🎯 Exploit Status

🛠️ Fix & Mitigation

✅ Official Fix

Instructions:

🔧 Temporary Workarounds

Disable follow_x_forwarded_for

Limit header size

🧯 If You Can't Patch

🔍 How to Verify

Check if Vulnerable:

Check Version:

Verify Fix Applied:

📡 Detection & Monitoring

Log Indicators:

Network Indicators:

SIEM Query:

📊 Metadata

🔗 References

📤 Share & Export

🔗 Related Vulnerabilities