CVE-2026-42356 in HTTP Server
Summary
by MITRE • 10/01/2026
Deployment of wrong handler vulnerability in Apache HTTP Server allows the target of some internal redirects from CGI programs to also be treated as CGI and executed. The target must already be in a directory enabled for CGI and have no other extension understood by mod_mime.
This issue affects Apache HTTP Server: from 2.4.60 through 2.4.68.
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Analysis
by VulDB Data Team • 10/03/2026
The vulnerability identified within the Apache HTTP Server, specifically affecting versions ranging from 2.4.60 to 2.4.68, represents a critical logic flaw in how the server handles internal redirects originating from Common Gateway Interface programs. This issue stems from an incorrect assignment or persistence of handler attributes during the request processing lifecycle. When a CGI script triggers an internal redirect, the Apache core is designed to reset certain context variables to ensure that subsequent requests are processed according to their new URI and configuration directives rather than inheriting properties from the previous request phase. However, in this specific scenario, the server fails to properly clear or override the handler associated with the original request when determining how to process the target of the redirect. This oversight allows a malicious actor who can control or influence the output of a CGI script to manipulate where that script redirects its execution flow and subsequently exploit the misconfigured state of the request handling mechanism.
From a technical perspective, this vulnerability relies on specific environmental conditions within the Apache configuration. The attack vector requires that the target URI of the internal redirect points to a directory explicitly enabled for CGI execution via directives such as ScriptAlias or Options ExecCGI. Furthermore, the file at the destination must lack any filename extension that is recognized by mod_mime for other purposes, such as HTML, CSS, or static content mapping. Under normal circumstances, if a valid MIME type handler were associated with the target file through its extension, the server would process it according to those specific rules. However, because no conflicting handlers are present due to the absence of understood extensions, and given that CGI execution is enabled for the directory, the flawed logic causes Apache to apply the CGI handler to this otherwise static or differently intended resource. This effectively bypasses standard access controls and content-type validations that would normally prevent arbitrary code execution on non-script files.
The operational impact of this vulnerability is severe, as it facilitates Remote Code Execution with the privileges of the web server process. An attacker who can inject a crafted redirect URL into a CGI application running under Apache HTTP Server can cause the server to execute arbitrary scripts or binaries located in directories designated for CGI execution but which were not intended to be executed via that specific request path. This could lead to full system compromise, data exfiltration, or lateral movement within the network infrastructure hosting the vulnerable service. The severity is compounded by the fact that it requires no authentication if the target directory and scripts are publicly accessible, although even authenticated scenarios pose significant risk due to the elevation of privileges inherent in CGI execution contexts. This aligns with CWE-94 Improper Control of Generation of Code or Script, as well as CWE-611 Improper Restriction of XML External Entity References when considering broader implications of input validation failures, though primarily it is a logic error classified under CWE-20 Poor Input Validation and Handling in the context of request routing.
In terms of threat modeling and detection, this vulnerability maps to MITRE ATT&CK techniques involving Command and Scripting Interpreter execution via web application attacks. Specifically, it relates to T1505 Server Software Component: Web Shell or similar mechanisms where an attacker leverages server-side script engines for unauthorized access. The exploitation typically involves crafting HTTP requests that trigger the internal redirect mechanism within a vulnerable CGI endpoint, ensuring the target path meets the directory and extension criteria described above. Security monitoring systems should look for unusual patterns of internal redirects originating from CGI endpoints to paths in ScriptAlias directories with minimal file extensions, as these may indicate attempted exploitation of this logic flaw.
Mitigation strategies must focus on immediate patching and configuration hardening. The primary remediation is to upgrade Apache HTTP Server to a version newer than 2.4.68 where the handler reset logic has been corrected during internal redirects. For environments unable to immediately update, administrators should review CGI configurations to ensure that directories enabled for ExecCGI do not contain files with ambiguous extensions or restrict access to sensitive scripts using additional authentication mechanisms such as Require valid-user directives combined with strong credential policies. Additionally, implementing strict input validation on all parameters passed to CGI programs can reduce the likelihood of an attacker successfully injecting malicious redirect targets. Regular security audits and penetration testing focused on web application logic flaws are recommended to identify similar misconfigurations in server-side processing pipelines before they can be exploited by adversaries seeking initial access or privilege escalation within compromised systems.