CVE-2010-1866 in PHP
Summary
by MITRE
The dechunk filter in PHP 5.3 through 5.3.2, when decoding an HTTP chunked encoding stream, allows context-dependent attackers to cause a denial of service (crash) and possibly trigger memory corruption via a negative chunk size, which bypasses a signed comparison, related to an integer overflow in the chunk size decoder.
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Analysis
by VulDB Data Team • 01/25/2025
The vulnerability identified as CVE-2010-1866 represents a critical flaw in PHP's HTTP chunked encoding processing mechanism that affects versions 5.3 through 5.3.2. This issue resides within the dechunk filter component responsible for handling HTTP chunked transfer encoding, a standard method for transmitting data in chunks over HTTP connections. The vulnerability stems from inadequate input validation and improper handling of chunk size parameters during the decoding process, creating a scenario where maliciously crafted chunked data can trigger unexpected behavior in the PHP runtime environment.
The technical root cause of this vulnerability lies in the integer overflow condition that occurs when processing negative chunk sizes within the chunk size decoder. When PHP encounters a chunk size that is negative, the system fails to properly validate this value against the expected unsigned integer range, allowing a signed comparison to be bypassed. This bypass enables attackers to manipulate the chunk size parameter in such a way that it wraps around to a large positive value due to integer overflow behavior, effectively causing the decoder to attempt processing an impossibly large chunk. The flaw specifically manifests in the dechunk filter's handling of the chunk size parsing logic, where the system does not adequately check for negative values or properly handle integer overflow conditions that can occur during the conversion from string representation to integer format.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enable memory corruption scenarios that could be exploited for more serious consequences. When an attacker sends HTTP requests containing maliciously formatted chunked data with negative chunk sizes, the PHP process may crash due to attempting to allocate memory for chunks that exceed system limits or cause buffer overflows. The vulnerability's context-dependent nature means that successful exploitation requires specific conditions such as the target application being configured to process chunked HTTP requests and the attacker having the ability to inject malicious data into the HTTP stream. This makes the vulnerability particularly dangerous in web applications that process user-supplied HTTP data, as it can be triggered through normal HTTP request processing without requiring special privileges or direct system access.
From a cybersecurity perspective, this vulnerability aligns with CWE-190, which describes integer overflow conditions, and demonstrates characteristics that could be mapped to ATT&CK technique T1499.004 for network denial of service attacks. The vulnerability's potential for memory corruption suggests it could be leveraged as a stepping stone for more advanced exploitation techniques, though the direct exploitability remains limited by the context-dependent nature of the attack vector. Organizations should prioritize immediate patching of affected PHP installations, as the vulnerability affects a core component of web application processing and can be exploited through standard HTTP traffic without requiring specialized tools or conditions. The fix implemented in later PHP versions typically involves adding proper validation of chunk size parameters and ensuring that negative values are properly rejected or handled without triggering integer overflow conditions. System administrators should also consider implementing network-level protections such as HTTP request filtering and monitoring for unusual chunked encoding patterns to detect potential exploitation attempts.
This vulnerability serves as a reminder of the importance of proper input validation in web application security, particularly in components that handle network protocol parsing. The issue demonstrates how seemingly simple protocol handling code can contain complex integer arithmetic vulnerabilities that can be exploited to cause system instability. Organizations should maintain robust patch management processes and conduct regular security assessments of their PHP installations to identify and remediate similar vulnerabilities that could potentially enable more serious exploits. The vulnerability also highlights the need for thorough testing of edge cases in protocol implementations, particularly around integer handling and boundary conditions that could be exploited by attackers.