CVE-2016-5093 in PHP
Summary
by MITRE
The get_icu_value_internal function in ext/intl/locale/locale_methods.c in PHP before 5.5.36, 5.6.x before 5.6.22, and 7.x before 7.0.7 does not ensure the presence of a '\0' character, which allows remote attackers to cause a denial of service (out-of-bounds read) or possibly have unspecified other impact via a crafted locale_get_primary_language call.
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Analysis
by VulDB Data Team • 09/13/2022
The vulnerability identified as CVE-2016-5093 represents a critical out-of-bounds read flaw within the Internationalization extension of PHP, specifically within the get_icu_value_internal function located in ext/intl/locale/locale_methods.c. This issue affects multiple PHP versions including those before 5.5.36, 5.6.x before 5.6.22, and 7.x before 7.0.7, creating a widespread impact across the PHP ecosystem. The vulnerability stems from inadequate input validation where the function fails to properly verify the presence of a null terminator character, which is essential for safe string processing operations. This flaw exists within the ICU (International Components for Unicode) integration that PHP uses for locale and internationalization support, making it particularly concerning for applications that handle user-provided locale data.
The technical exploitation of this vulnerability occurs when a crafted locale_get_primary_language function call is made with malformed input data. The absence of proper null termination checking in the get_icu_value_internal function allows attackers to manipulate memory access patterns and potentially trigger out-of-bounds read operations. This type of vulnerability falls under CWE-129, which specifically addresses insufficient validation of length of inputs, and is closely related to CWE-787, out-of-bounds write conditions that can occur when improper bounds checking leads to memory corruption. The vulnerability can be leveraged through the PHP Internationalization extension, which is commonly enabled in web applications that require locale handling, making it an attractive target for remote attackers seeking to disrupt service availability or potentially execute arbitrary code through memory corruption exploits.
From an operational impact perspective, this vulnerability enables remote attackers to cause denial of service conditions by triggering out-of-bounds memory reads that may crash the PHP process or cause unpredictable behavior in the web application. The potential for unspecified other impacts suggests that under certain conditions, attackers might be able to extract sensitive information from memory or potentially escalate privileges depending on the system configuration. The attack vector requires only a single malformed function call, making it particularly dangerous as it can be exploited through web interfaces or any application layer that processes user-provided locale information. This vulnerability aligns with ATT&CK technique T1059.007, which involves the use of scripting languages, and T1499.004, which covers network denial of service, as it can be used to disrupt web application availability through controlled memory access violations.
The recommended mitigation strategy involves upgrading to the patched versions of PHP where this vulnerability has been addressed. System administrators should prioritize updating their PHP installations to versions 5.5.36, 5.6.22, or 7.0.7 respectively, depending on their current version. Additionally, implementing proper input validation at the application level can provide an additional layer of defense by sanitizing locale data before passing it to the internationalization functions. Organizations should also consider implementing network-level protections such as web application firewalls that can detect and block suspicious function calls. The vulnerability demonstrates the importance of proper memory management and input validation in language extensions, particularly those that interface with complex libraries like ICU. Regular security auditing of PHP extensions and maintaining up-to-date software versions remain critical defensive measures against similar vulnerabilities that could arise from inadequate bounds checking in string handling operations.