CVE-2016-1000104 – This vulnerability in mod_fcgid's FcgidPassHead... (How to Fix)

Q: What is the severity of CVE-2016-1000104?

CVE-2016-1000104 has a CVSS score of 8.8 (HIGH). This vulnerability in mod_fcgid's FcgidPassHeader Proxy allows attackers to bypass security restrictions by manipulating HTTP headers. It affects Apache servers using mod_fcgid versions before the fix, potentially enabling unauthorized access or privilege escalation.

📋 TL;DR

This vulnerability in mod_fcgid's FcgidPassHeader Proxy allows attackers to bypass security restrictions by manipulating HTTP headers. It affects Apache servers using mod_fcgid versions before the fix, potentially enabling unauthorized access or privilege escalation.

💻 Affected Systems

Products:

mod_fcgid

Versions: All versions through 2016-07-07

Operating Systems: Linux, Unix systems running Apache with mod_fcgid

Default Config Vulnerable: ⚠️ Yes

Notes: Requires mod_fcgid with FcgidPassHeader configuration. Common in shared hosting environments.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete server compromise allowing remote code execution, data theft, or service disruption.

🟠

Likely Case

Unauthorized access to restricted resources or privilege escalation within the web application.

🟢

If Mitigated

Limited impact with proper network segmentation and minimal exposed attack surface.

🌐 Internet-Facing: HIGH - Directly exploitable via HTTP requests to vulnerable web servers.

🏢 Internal Only: MEDIUM - Requires internal network access but still exploitable if vulnerable systems are reachable.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires sending specially crafted HTTP headers to vulnerable endpoints.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Versions after 2016-07-07

Vendor Advisory: http://www.openwall.com/lists/oss-security/2016/07/18/6

Restart Required: Yes

Instructions:

1. Update mod_fcgid to version after 2016-07-07. 2. Restart Apache service. 3. Verify the update with version check.

🔧 Temporary Workarounds

Disable FcgidPassHeader

linux

Remove or comment out FcgidPassHeader directives in Apache configuration

# Edit Apache config (e.g., /etc/httpd/conf.d/fcgid.conf)
# Comment: #FcgidPassHeader Authorization
# Restart: systemctl restart httpd

🧯 If You Can't Patch

Implement strict network ACLs to limit access to vulnerable servers
Deploy WAF rules to block malicious header manipulation attempts

🔍 How to Verify

Check if Vulnerable:

Check mod_fcgid version and configuration for FcgidPassHeader usage

Check Version:

httpd -M 2>/dev/null | grep fcgid && grep -i version /path/to/mod_fcgid.so

Verify Fix Applied:

Confirm mod_fcgid version is after 2016-07-07 and test header manipulation

📡 Detection & Monitoring

Log Indicators:

Unusual HTTP header patterns in access logs
Failed authentication attempts with manipulated headers

Network Indicators:

HTTP requests with abnormal header structures
Traffic to mod_fcgid endpoints with suspicious headers

SIEM Query:

source="apache_access" AND (header="*Authorization*" OR header="*Proxy*" OR header="*Fcgid*")

📊 Metadata

CVE ID: CVE-2016-1000104

CVSS v3 Score: 8.8 (HIGH)

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

CWE: CWE-20

Published: December 3, 2019

Last Updated: November 21, 2024

🔗 References

http://lists.opensuse.org/opensuse-updates/2016-08/msg00084.html Mailing List,Third Party Advisory
http://www.openwall.com/lists/oss-security/2016/07/18/6
http://www.securityfocus.com/bid/91822
https://www.tenable.com/security/tns-2017-04
http://lists.opensuse.org/opensuse-updates/2016-08/msg00084.html Mailing List,Third Party Advisory
http://www.openwall.com/lists/oss-security/2016/07/18/6
http://www.securityfocus.com/bid/91822
https://www.tenable.com/security/tns-2017-04

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