CVE-2011-3607 in HTTP Server
Summary
by MITRE
Integer overflow in the ap_pregsub function in server/util.c in the Apache HTTP Server 2.0.x through 2.0.64 and 2.2.x through 2.2.21, when the mod_setenvif module is enabled, allows local users to gain privileges via a .htaccess file with a crafted SetEnvIf directive, in conjunction with a crafted HTTP request header, leading to a heap-based buffer overflow.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 08/10/2024
The vulnerability identified as CVE-2011-3607 represents a critical integer overflow flaw within the Apache HTTP Server software that affects versions 2.0.x through 2.0.64 and 2.2.x through 2.2.21. This issue stems from the ap_pregsub function located in server/util.c, which is responsible for processing regular expression substitutions within the server's configuration handling mechanisms. The vulnerability becomes exploitable when the mod_setenvif module is enabled, creating a dangerous combination that allows local attackers to escalate privileges through carefully crafted malicious configurations.
The technical flaw manifests as an integer overflow condition that occurs during the processing of SetEnvIf directives within .htaccess files. When a malicious user creates a crafted SetEnvIf directive combined with a specially constructed HTTP request header, the integer overflow in the ap_pregsub function leads to heap-based buffer overflow conditions. This overflow occurs because the function fails to properly validate input sizes before performing memory allocation operations, allowing an attacker to manipulate the memory layout of the Apache process and potentially execute arbitrary code with the privileges of the web server.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with a pathway to compromise the entire web server infrastructure. The attack requires local access to the server filesystem to place the malicious .htaccess file, but once deployed, the vulnerability can be triggered through normal HTTP traffic. This makes the exploit particularly dangerous in shared hosting environments or when administrators inadvertently allow write access to web directories. The heap-based buffer overflow creates opportunities for memory corruption that can be leveraged for code execution, potentially allowing attackers to establish persistent access to the compromised system.
Security professionals should note that this vulnerability aligns with CWE-190, which specifically addresses integer overflow conditions that can lead to buffer overflows. The exploit technique follows patterns commonly associated with privilege escalation attacks in web server environments and can be mapped to ATT&CK techniques related to privilege escalation and execution through configuration files. Organizations should prioritize immediate patching of affected Apache versions and implement proper file access controls to prevent unauthorized .htaccess file modifications. Additionally, monitoring for unusual SetEnvIf directive usage and implementing network-based intrusion detection systems can help identify potential exploitation attempts before they succeed in compromising server integrity.