Tech Stack: Apache HTTP Server (httpd)

Date(s) Issued: Published: 03/24/2018; Last Modified: 12/09/2024

Criticality: CVSS v3 Score: 8.1 – HIGH

Overview: CVE-2017-15715 is a vulnerability in Apache HTTP Server versions 2.4.0 through 2.4.29, where the <FilesMatch> directive’s regular expression could incorrectly match the $ character to a newline in a malicious filename, rather than matching only the end of the filename. This flaw could be exploited in environments that block uploads of certain files based on filename patterns, allowing attackers to bypass such restrictions by appending a newline character to the filename.

Solution/Mitigation:

1. Upgrade Apache HTTP Server:
   • Version: Upgrade to Apache HTTP Server version 2.4.30 or later, where this issue has been resolved. Ensure that all instances of the server are updated to prevent exploitation. Apache HTTP Server
2. Review and Update Configuration:
   • Regular Expressions: Examine the use of the <FilesMatch> directive in your server configuration. Ensure that regular expressions are correctly defined to match filenames as intended, and consider using more explicit patterns to prevent unintended matches.
   • Input Validation: Implement robust input validation to sanitize filenames and detect anomalies, such as unexpected newline characters, that could be used to bypass security measures.
3. Monitor and Audit:
   • Log Analysis: Regularly review server logs for unusual file upload activities, especially filenames containing newline characters or other suspicious patterns. Implement automated alerts for such anomalies to facilitate prompt investigation.
   • Access Controls: Ensure that appropriate access controls are in place to restrict file uploads to authorized users and that file upload directories have the necessary permissions to prevent unauthorized access.
4. Apply Security Patches:
   • Operating System Updates: Keep your operating system and all installed packages up to date with the latest security patches provided by your distribution. For instance, Debian has addressed this issue in DSA-4164. Debian Security Tracker

Confirmation & Additional Information:

• Verification: After applying the upgrade and configuration changes, test the server to confirm that the vulnerability has been mitigated. Attempt to upload files with filenames containing newline characters to ensure that such uploads are appropriately blocked if intended.
• Stay Updated: Regularly consult official Apache HTTP Server security advisories and your operating system’s security bulletins to stay informed about any new vulnerabilities or patches. Subscribe to relevant mailing lists or RSS feeds for timely notifications.
• Official Resources:
  • Apache HTTP Server Security Vulnerabilities: Apache HTTP Server
  • National Vulnerability Database Entry: NVD
  • Debian Security Tracker: Debian Security Tracker