CVE-2018-1283 in HTTP Server
Summary
by MITRE
In Apache httpd 2.4.0 to 2.4.29, when mod_session is configured to forward its session data to CGI applications (SessionEnv on, not the default), a remote user may influence their content by using a "Session" header. This comes from the "HTTP_SESSION" variable name used by mod_session to forward its data to CGIs, since the prefix "HTTP_" is also used by the Apache HTTP Server to pass HTTP header fields, per CGI specifications.
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Analysis
by VulDB Data Team • 02/24/2023
The vulnerability described in CVE-2018-1283 represents a critical security flaw in the Apache HTTP Server version 2.4.0 through 2.4.29 that arises from improper handling of session data forwarding to CGI applications. This issue specifically affects deployments where the mod_session module is configured with SessionEnv enabled, creating a dangerous overlap between session management and HTTP header processing. The flaw stems from the naming convention used by mod_session to forward session data to CGI applications, where session data is prefixed with "HTTP_" to align with CGI specifications, inadvertently creating a pathway for header manipulation.
The technical implementation of this vulnerability occurs when mod_session is configured to forward session data to CGI applications through the SessionEnv directive, which enables the transfer of session information via environment variables. The mod_session module uses the "HTTP_" prefix when forwarding session data to CGI applications, but this prefix is also recognized by the Apache HTTP Server as a special indicator for HTTP header fields in CGI environments. This dual interpretation creates a scenario where a remote attacker can manipulate session data by injecting malicious content through HTTP headers, specifically targeting the Session header that gets processed by mod_session and subsequently forwarded to CGI applications.
The operational impact of this vulnerability is significant as it allows remote attackers to influence the content processed by CGI applications through crafted HTTP headers. This represents a privilege escalation and data manipulation attack vector that can compromise session integrity and potentially lead to unauthorized access or data corruption within applications that rely on mod_session for session management. The vulnerability essentially enables header injection attacks that can bypass normal security controls and manipulate application behavior through session data manipulation.
This vulnerability aligns with CWE-116, which addresses improper encoding or escaping of output, and represents a form of header injection that can be classified under ATT&CK technique T1071.3 for application layer protocol. The flaw demonstrates how seemingly innocuous configuration options can create security risks when combined with standard server processing behaviors. Organizations using Apache HTTP Server with mod_session configured for CGI session forwarding are particularly vulnerable, as the default configuration does not enable this behavior but can be easily misconfigured by administrators. The attack surface is expanded when applications process session data forwarded through CGI environments, making this vulnerability particularly dangerous in complex web application architectures.
Mitigation strategies for CVE-2018-1283 focus on disabling the SessionEnv directive when mod_session is configured for CGI forwarding, as this removes the problematic data forwarding mechanism that enables the attack. Administrators should also consider upgrading to Apache HTTP Server version 2.4.30 or later, where this vulnerability has been addressed through improved session data handling and validation. Additionally, implementing proper input validation and sanitization within CGI applications that receive session data can provide defense-in-depth protection. Network-level controls such as web application firewalls can also help detect and block malicious header injection attempts, though the most effective mitigation remains proper configuration of mod_session to avoid the vulnerable data forwarding behavior. Security monitoring should include detection of unusual Session header patterns that might indicate exploitation attempts.