CVE-2026-90937 in Froxlor
Summary
by MITRE • 09/14/2026
froxlor versions before 2.2.5 fail to validate newline characters in subdomain redirect URLs, allowing authenticated customers to inject arbitrary nginx or Apache configuration directives. Attackers can supply URLs containing literal newlines that are written verbatim into vhost config files during cron rebuild, enabling web server configuration corruption, denial of service, or hijacking of HTTP responses across hosted domains.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 09/14/2026
The vulnerability identified in Froxlor versions prior to 2.2.5 represents a critical server-side request forgery and code injection flaw rooted in insufficient input validation within the subdomain redirect functionality. As an authenticated customer user, one possesses the ability to configure redirection rules for their hosted domains through the administrative interface. The core technical failure lies in the application's handling of newline characters embedded within these URL inputs. Instead of sanitizing or rejecting control characters such as carriage returns and line feeds, the software passes them verbatim into the configuration generation process. This lack of strict validation allows an attacker to break out of the intended single-line directive structure expected by the web server configuration files, thereby injecting arbitrary additional lines that are interpreted directly by nginx or Apache during subsequent cron job executions that rebuild virtual host configurations.
This flaw effectively grants authenticated users a form of local privilege escalation against the web server's configuration logic. By crafting malicious URLs containing literal newlines, an attacker can append custom directives to the vhost files for any domain hosted on the same Froxlor instance. The operational impact is severe and multifaceted. First, it enables denial of service by corrupting the syntax of critical configuration files, which prevents the web server from starting or reloading properly, thereby taking down all services dependent on that server. Second, it allows for HTTP response hijacking across hosted domains. An attacker can inject directives such as proxy_pass headers to redirect traffic to a malicious external server, facilitating phishing attacks or data exfiltration under the guise of legitimate domain names. Furthermore, this could potentially lead to cross-site scripting if injected content includes script tags that are later rendered by browsers visiting those hijacked endpoints, although the primary vector is configuration manipulation rather than direct client-side execution.
From a classification perspective, this vulnerability aligns with CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component and CWE-93 Improper Neutralization of CRLF Sequences. The attack pattern corresponds to ATT&CK technique T1059 Command and Scripting Interpreter via system configuration files or T1190 Exploit Public-Facing Application, specifically leveraging the application's administrative features for unauthorized control over infrastructure components. The severity is heightened by the fact that authentication is required, but since Froxlor manages multiple customer accounts on a single server, compromise of one low-privilege account can lead to widespread disruption or espionage across all hosted entities.
Mitigation strategies must prioritize immediate patching to version 2.2.5 or later where this validation logic has been corrected. In the interim, administrators should enforce strict input filtering at the application layer by rejecting any user-supplied data containing newline characters before it reaches the configuration generation module. Additionally, implementing principle of least privilege for web server processes can limit the damage if a misconfiguration occurs, though this is secondary to fixing the root cause. Regular auditing of generated vhost files and monitoring cron job logs for syntax errors can also help in detecting exploitation attempts early. It is crucial to ensure that all Froxlor instances are updated promptly as these configuration injection flaws pose significant risks to multi-tenant hosting environments where trust boundaries between customers must be strictly maintained.