CVE-2015-8873 in PHP
Summary
by MITRE
Stack consumption vulnerability in Zend/zend_exceptions.c in PHP before 5.4.44, 5.5.x before 5.5.28, and 5.6.x before 5.6.12 allows remote attackers to cause a denial of service (segmentation fault) via recursive method calls.
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Analysis
by VulDB Data Team • 08/19/2022
The vulnerability identified as CVE-2015-8873 represents a critical stack consumption issue affecting PHP versions prior to specific patch releases. This flaw exists within the Zend/zend_exceptions.c file of the PHP engine, which handles exception processing and method call management. The vulnerability manifests when recursive method calls are processed, leading to excessive stack memory consumption that eventually results in segmentation faults and system crashes. The issue impacts multiple PHP version streams including 5.4.x, 5.5.x, and 5.6.x, making it particularly widespread across the PHP ecosystem during that time period.
The technical root cause of this vulnerability lies in the improper handling of recursive method calls within PHP's exception processing mechanism. When a recursive method call occurs, the PHP interpreter's stack management fails to properly track or limit the depth of recursion, allowing malicious inputs to consume excessive stack space. This behavior directly maps to CWE-674, which describes "Uncontrolled Recursion" in software systems. The flaw operates at the interpreter level where the Zend Engine processes method calls and exception handling, making it particularly dangerous as it can be triggered through normal PHP code execution patterns.
From an operational perspective, this vulnerability creates a significant denial of service risk for web applications running affected PHP versions. Remote attackers can exploit this weakness by crafting specific inputs that trigger recursive method calls, causing the web server to crash or become unresponsive. The segmentation fault that occurs represents a complete system failure that can be leveraged for service disruption attacks. This vulnerability aligns with ATT&CK technique T1499.004, which covers "Endpoint Denial of Service" through resource exhaustion. The impact extends beyond simple service interruption as it can potentially be used to crash entire web applications, affecting availability for legitimate users and potentially exposing underlying system vulnerabilities.
The exploitation of this vulnerability requires minimal privileges and can be executed remotely through standard web application interfaces. Attackers need only send crafted requests that trigger recursive method calls to the vulnerable PHP interpreter, making it particularly dangerous for publicly accessible web applications. The vulnerability affects both development and production environments, with the patch releases (5.4.44, 5.5.28, and 5.6.12) addressing the stack consumption issue by implementing proper recursion depth limits and improved stack management. Organizations should prioritize immediate patching of affected systems to prevent exploitation, as the vulnerability provides no legitimate access to system resources beyond causing service disruption. Security monitoring should include detection of unusual stack consumption patterns and recursive call sequences that may indicate attempted exploitation of this vulnerability.