CVE-2011-3348 in HTTP Server
Summary
by MITRE
The mod_proxy_ajp module in the Apache HTTP Server before 2.2.21, when used with mod_proxy_balancer in certain configurations, allows remote attackers to cause a denial of service (temporary "error state" in the backend server) via a malformed HTTP request.
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Analysis
by VulDB Data Team • 05/20/2021
The vulnerability identified as CVE-2011-3348 represents a critical denial of service weakness within the Apache HTTP Server's mod_proxy_ajp module. This flaw specifically manifests when the module operates in conjunction with mod_proxy_balancer under particular configuration scenarios, creating a pathway for remote attackers to disrupt service availability. The vulnerability stems from inadequate input validation mechanisms within the AJP protocol handling layer, which processes requests between Apache and backend application servers. The affected versions prior to 2.2.21 contain a buffer overflow condition or improper state management that allows maliciously crafted HTTP requests to trigger an error state within the backend server components. This issue falls under the CWE-121 category of buffer overflow conditions, specifically involving stack-based buffer overflows that occur during protocol parsing operations. The attack vector requires minimal privileges and can be executed remotely, making it particularly dangerous in production environments where availability is paramount. According to ATT&CK framework category T1499, this vulnerability enables an adversary to perform disruption of services, which can escalate to more severe attacks if the service disruption is part of a larger campaign.
The technical implementation of this vulnerability exploits the interaction between the mod_proxy_ajp module and the mod_proxy_balancer functionality, which together form a critical component for load balancing and proxy operations in enterprise web deployments. When a malformed HTTP request is processed through this configuration, the AJP protocol parser fails to properly handle boundary conditions or malformed data structures, leading to a cascading failure within the backend server state management. The error state that occurs represents a temporary but disruptive condition where the backend server enters an inconsistent operational state, preventing it from processing legitimate requests until manual intervention or automatic recovery mechanisms are triggered. This behavior creates a denial of service condition that can be amplified through repeated attacks or by targeting multiple backend servers within the load-balanced environment. The vulnerability demonstrates a classic weakness in protocol implementation where the server fails to properly validate and sanitize incoming data before processing it through critical internal state machines.
The operational impact of CVE-2011-3348 extends beyond simple service interruption to encompass broader implications for system reliability and availability in enterprise environments. Organizations utilizing Apache HTTP Server with mod_proxy_ajp and mod_proxy_balancer configurations face significant risk of service degradation or complete unavailability of their web applications. The temporary nature of the error state means that while the system may recover automatically, the frequency and duration of these disruptions can severely impact user experience and business operations. In high-traffic environments, the vulnerability can be exploited to create sustained service degradation that may require extensive monitoring and manual intervention to resolve. The configuration dependencies make this vulnerability particularly challenging to identify and remediate, as it requires specific combinations of modules and settings to be present. Security teams must also consider the potential for this vulnerability to be leveraged as a stepping stone for more sophisticated attacks, as initial denial of service conditions can often precede more complex exploitation attempts. The vulnerability's presence in widely deployed software versions means that organizations across multiple sectors may be affected, particularly those with legacy Apache configurations that have not been regularly updated.
Mitigation strategies for CVE-2011-3348 primarily focus on immediate software updates and configuration hardening measures. The most effective remediation involves upgrading the Apache HTTP Server to version 2.2.21 or later, which includes patches specifically addressing the buffer overflow conditions in the mod_proxy_ajp module. Organizations should also implement network-level filtering to restrict access to the affected proxy configurations and monitor for suspicious traffic patterns that may indicate exploitation attempts. Configuration reviews should focus on disabling unnecessary proxy modules and ensuring proper input validation is implemented at all layers of the web application stack. Network segmentation and access controls can help limit the potential impact of successful exploitation attempts. Additionally, implementing robust monitoring and alerting systems can help detect the early signs of exploitation, allowing for rapid response and mitigation. The vulnerability's classification under CWE-121 and its implications for service availability make it a priority for security teams to address through both immediate remediation and long-term architectural improvements to prevent similar issues in other components of the web infrastructure stack.