CVE-2011-1148 in PHP
Summary
by MITRE
Use-after-free vulnerability in the substr_replace function in PHP 5.3.6 and earlier allows context-dependent attackers to cause a denial of service (memory corruption) or possibly have unspecified other impact by using the same variable for multiple arguments.
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Analysis
by VulDB Data Team • 10/19/2021
The CVE-2011-1148 vulnerability represents a critical use-after-free flaw in PHP's substr_replace function affecting versions 5.3.6 and earlier. This vulnerability arises from improper memory management within the function's argument handling mechanism, where the same variable can be passed multiple times as arguments without proper validation of memory references. The flaw specifically manifests when the substr_replace function processes input parameters that reference the same memory location, creating conditions where freed memory can be accessed or modified by subsequent operations. This type of vulnerability falls under the CWE-416 category of Use After Free, which is classified as a severe memory corruption issue that can lead to unpredictable behavior and system instability.
The technical exploitation of this vulnerability occurs when an attacker crafts malicious input that causes the substr_replace function to process identical variable references across multiple arguments. During normal execution, PHP's internal memory management allocates memory for variables and maintains reference counts to track usage. When the same variable is passed multiple times to substr_replace, the function's internal logic may incorrectly handle memory deallocation, leading to scenarios where memory that has been freed is subsequently accessed or modified. This creates a race condition where freed memory blocks can be reallocated for other purposes while the function still maintains references to them, resulting in memory corruption that can manifest as application crashes, data corruption, or potentially arbitrary code execution depending on the memory layout and timing conditions.
From an operational impact perspective, this vulnerability presents significant risks to web applications running vulnerable PHP versions, as it can be exploited to cause denial of service conditions that render applications unavailable to legitimate users. The potential for unspecified other impacts means that attackers could potentially leverage this memory corruption to execute arbitrary code, bypass security controls, or escalate privileges within the affected system. The context-dependent nature of the vulnerability means that exploitation requires specific conditions to be met, but once achieved, the impact can be severe enough to compromise entire web servers or application environments. Organizations running PHP applications are particularly vulnerable since the substr_replace function is commonly used in web applications for string manipulation tasks, making this vulnerability exploitable through various attack vectors including web-based input processing.
Security mitigations for CVE-2011-1148 primarily focus on immediate patching and version upgrades to PHP 5.3.7 or later, where the memory management issues within substr_replace have been resolved through improved reference counting and memory allocation handling. Additionally, organizations should implement input validation measures that prevent the reuse of variables in potentially problematic function calls, though this approach is less reliable than patching the underlying vulnerability. The vulnerability aligns with ATT&CK technique T1059.007 for Scripting and T1499.004 for Network Denial of Service, as it can be leveraged to cause service disruption and potentially enable further exploitation. Organizations should also consider implementing runtime monitoring and anomaly detection systems to identify suspicious patterns in function calls that might indicate exploitation attempts, particularly focusing on the substr_replace function and similar string manipulation operations that may be vulnerable to similar memory management issues.