CVE-2017-12932 in PHP
Summary
by MITRE
ext/standard/var_unserializer.re in PHP 7.0.x through 7.0.22 and 7.1.x through 7.1.8 is prone to a heap use after free while unserializing untrusted data, related to improper use of the hash API for key deletion in a situation with an invalid array size. Exploitation of this issue can have an unspecified impact on the integrity of PHP.
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Analysis
by VulDB Data Team • 12/16/2022
The vulnerability identified as CVE-2017-12932 represents a critical heap use after free condition within PHP's serialization unmarshaling process. This flaw exists in the ext/standard/var_unserializer.re component of PHP versions 7.0.x through 7.0.22 and 7.1.x through 7.1.8, where the improper handling of hash API operations during key deletion creates exploitable memory management issues. The vulnerability specifically manifests when PHP processes untrusted serialized data through the unserialize() function, making it particularly dangerous in web applications that accept user input for deserialization operations. The underlying issue stems from the incorrect interaction between the hash table management system and array size validation during the unserialization process, creating opportunities for memory corruption that can be leveraged by attackers.
The technical exploitation of this vulnerability occurs through carefully crafted serialized data that manipulates the internal hash table structures during deserialization. When PHP attempts to delete keys from a hash table while processing invalid array sizes, the memory management system fails to properly handle the cleanup operations, leading to situations where freed memory locations are accessed or overwritten. This improper use of the hash API creates a scenario where attackers can control the memory layout and potentially execute arbitrary code or cause denial of service conditions. The vulnerability aligns with CWE-416, which describes use after free conditions, and represents a classic memory corruption issue that can be exploited through the manipulation of serialized data structures. The attack vector specifically targets the unserialize() function's handling of malicious input, making it particularly relevant to applications that process external data without proper validation.
The operational impact of CVE-2017-12932 extends beyond simple denial of service scenarios to encompass potential remote code execution capabilities. Attackers who can influence the data being unserialized can manipulate the heap memory layout to achieve arbitrary code execution, making this vulnerability particularly dangerous in web applications where user input flows directly into deserialization operations. The vulnerability affects PHP applications that accept serialized data from external sources, including but not limited to session data, API responses, or database records that may contain serialized objects. This flaw can be exploited across various attack surfaces where PHP's unserialize() function is utilized, potentially compromising entire web applications and server environments. The unspecified impact mentioned in the original description reflects the wide range of possible consequences, from data corruption to full system compromise, depending on the specific exploitation context and target environment.
Mitigation strategies for CVE-2017-12932 require immediate patching of affected PHP versions to the latest stable releases that contain the necessary fixes for the hash table management and memory cleanup operations. Organizations should implement strict input validation and sanitization measures to prevent untrusted data from reaching the unserialize() function, particularly in scenarios where user input flows into deserialization operations. The implementation of secure coding practices, including avoiding direct unserialization of user-provided data and using alternative serialization formats that do not expose similar vulnerabilities, provides additional defense layers. Security monitoring should focus on detecting unusual patterns in serialization operations and implementing proper access controls to limit the exposure of deserialization endpoints. The vulnerability demonstrates the importance of proper memory management in interpreted languages and reinforces the need for comprehensive security testing of serialization functions. Organizations should also consider implementing runtime protections such as address space layout randomization and stack canaries to make exploitation more difficult, while maintaining regular security updates to address similar vulnerabilities in the broader PHP ecosystem.