CVE-2007-1649 in PHP
Summary
by MITRE
PHP 5.2.1 allows context-dependent attackers to read portions of heap memory by executing certain scripts with a serialized data input string beginning with S:, which does not properly track the number of input bytes being processed.
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Analysis
by VulDB Data Team • 01/29/2025
The vulnerability described in CVE-2007-1649 represents a critical heap memory disclosure issue within PHP version 5.2.1 that arises from improper handling of serialized data structures. This flaw specifically manifests when PHP processes serialized data strings that begin with the character sequence S:, which indicates a serialized string in PHP's serialization format. The vulnerability stems from the serialization engine's failure to accurately track the number of input bytes being processed during the deserialization operation, creating a condition where adjacent heap memory can be inadvertently exposed to attackers.
The technical exploitation of this vulnerability occurs through crafted serialized data inputs that manipulate the parsing logic within PHP's unserialize function. When PHP encounters a serialized string beginning with S:, it attempts to parse the string content while maintaining internal counters for byte processing. However, due to the improper tracking mechanism, the parser can read beyond the intended boundaries of the serialized data, effectively accessing and potentially exposing portions of the heap memory that contains sensitive information such as stack contents, other variables, or even cryptographic keys. This memory disclosure vulnerability operates at the level of the PHP interpreter's internal memory management, making it particularly dangerous for applications that process untrusted input through serialization mechanisms.
The operational impact of CVE-2007-1649 extends beyond simple information disclosure, as the leaked heap memory can contain sensitive data that could be leveraged for more sophisticated attacks. Attackers can use this vulnerability to gather information about the application's memory layout, potentially enabling them to craft more effective exploitation techniques or to bypass security mechanisms that rely on memory randomization. The context-dependent nature of this vulnerability means that successful exploitation requires specific conditions where the attacker can control the serialized input, typically through web application parameters, file uploads, or other input vectors that eventually reach PHP's unserialize function. This vulnerability directly relates to CWE-125, which describes "Out-of-bounds Read" conditions, and aligns with ATT&CK technique T1552.001 for "Unsecured Credentials" and T1068 for "Exploitation for Privilege Escalation" when combined with other attack vectors.
Mitigation strategies for this vulnerability primarily focus on immediate patching of affected PHP installations to versions that properly implement byte tracking during serialization operations. Organizations should implement strict input validation and sanitization measures for all data that passes through PHP's unserialize function, particularly when processing external or user-controlled input. The implementation of proper access controls and the principle of least privilege can help limit the impact of successful exploitation attempts. Additionally, monitoring systems should be configured to detect unusual patterns in serialized data processing, and application-level security measures such as disabling unnecessary serialization functions or implementing custom serialization handlers can provide additional defense-in-depth layers. The vulnerability also underscores the importance of regular security assessments and staying current with security patches, as this issue was resolved in subsequent PHP releases through improved memory management and serialization parsing logic.