CVE-2026-90937 Overview
CVE-2026-90937 is a configuration injection vulnerability in Froxlor server management panel versions before 2.2.5. The flaw stems from missing validation of newline characters in subdomain redirect URLs. Authenticated customers can inject arbitrary nginx or Apache configuration directives that are written verbatim into vhost configuration files during scheduled cron rebuilds. Successful exploitation leads to web server configuration corruption, denial of service, or hijacking of HTTP responses across all hosted domains on the affected server. The vulnerability is classified under [CWE-93] Improper Neutralization of CRLF Sequences.
Critical Impact
A low-privileged Froxlor customer account can inject configuration directives that impact every domain hosted on the server, including response hijacking and full web service disruption.
Affected Products
- Froxlor server management panel versions prior to 2.2.5
- nginx vhost configurations generated by Froxlor
- Apache vhost configurations generated by Froxlor
Discovery Timeline
- 2026-09-14 - CVE-2026-90937 published to NVD
- 2026-09-16 - Last updated in NVD database
Technical Details for CVE-2026-90937
Vulnerability Analysis
Froxlor allows customers to configure subdomain redirects through its web interface. The application stores the supplied redirect URL and later injects it into nginx or Apache vhost configuration files when the configuration rebuild cron job runs. Versions before 2.2.5 do not strip or reject literal newline characters (\n, \r\n) submitted in the redirect URL field.
When the cron job regenerates vhost files, the untrusted URL is written directly into directives such as return 301 (nginx) or Redirect (Apache). Embedded newlines terminate the directive early and allow subsequent lines to be interpreted as additional configuration statements. The resulting configuration is loaded when the web server reloads, applying attacker-controlled directives across the shared server.
Root Cause
The root cause is missing input neutralization of CRLF sequences before untrusted data is serialized into a structured configuration file. Froxlor treats the redirect URL as opaque text and relies on the web server parser to interpret it. Because nginx and Apache configuration syntax is line-oriented, any embedded newline becomes a directive boundary. The flaw is a classic CRLF injection ([CWE-93]) applied to configuration file generation rather than HTTP responses.
Attack Vector
An authenticated Froxlor customer submits a subdomain redirect containing URL-encoded or literal newline characters followed by attacker-chosen configuration directives. The malicious payload is stored in the Froxlor database and remains dormant until the next configuration rebuild cron cycle. Once cron writes the vhost file and reloads nginx or Apache, the injected directives take effect. Attackers can insert server blocks, override location handlers, redirect traffic for unrelated tenant domains, or introduce syntax errors that prevent the web server from starting.
No verified public exploit code has been published. See the Froxlor GitHub Security Advisory and the VulnCheck advisory for additional technical detail.
Detection Methods for CVE-2026-90937
Indicators of Compromise
- Unexpected server, location, Redirect, or RewriteRule directives in generated vhost files under Froxlor's nginx or Apache configuration directories.
- Subdomain redirect URL records in the Froxlor database containing %0a, %0d, or literal CR/LF byte sequences.
- nginx or Apache reload failures logged immediately after a Froxlor cron rebuild cycle.
- HTTP responses on hosted domains that redirect to unexpected destinations not configured by the domain owner.
Detection Strategies
- Diff generated vhost configuration files against a baseline produced by a known-good Froxlor rebuild and flag any unexpected directives.
- Audit the Froxlor panel_domains and related subdomain redirect tables for URL values containing newline byte sequences.
- Monitor nginx -t and apachectl configtest exit codes during cron rebuild windows and alert on non-zero results.
Monitoring Recommendations
- Enable file integrity monitoring on Froxlor-managed vhost directories such as /etc/nginx/sites-enabled/ and /etc/apache2/sites-enabled/.
- Capture and centralize web server error logs to correlate configuration reload failures with Froxlor cron execution.
- Review Froxlor customer activity logs for recent subdomain redirect changes when configuration anomalies appear.
How to Mitigate CVE-2026-90937
Immediate Actions Required
- Upgrade Froxlor to version 2.2.5 or later on all managed servers.
- Audit existing subdomain redirect entries for embedded newline characters and remove malicious records before triggering the next rebuild.
- Restrict Froxlor customer account creation and review recently created accounts for suspicious redirect configurations.
Patch Information
The issue is fixed in Froxlor 2.2.5. Refer to the Froxlor GitHub Security Advisory GHSA-c3p2-mj7v-5mrc for the official patch and upgrade instructions. Apply the update before the next scheduled configuration rebuild cron runs.
Workarounds
- Temporarily disable the subdomain redirect feature for customers until the upgrade is applied.
- Insert a pre-commit hook or wrapper around the Froxlor cron rebuild that validates generated vhost files with nginx -t or apachectl configtest and aborts reload on failure.
- Sanitize the redirect URL column in the Froxlor database by rejecting or stripping any row containing \r or \n byte values.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
