CVE-2016-6294 in macOS
Summary
by MITRE
The locale_accept_from_http function in ext/intl/locale/locale_methods.c in PHP before 5.5.38, 5.6.x before 5.6.24, and 7.x before 7.0.9 does not properly restrict calls to the ICU uloc_acceptLanguageFromHTTP function, which allows remote attackers to cause a denial of service (out-of-bounds read) or possibly have unspecified other impact via a call with a long argument.
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Analysis
by VulDB Data Team • 09/20/2022
The vulnerability identified as CVE-2016-6294 affects PHP versions prior to specific patches, specifically impacting the locale_accept_from_http function within the intl extension. This flaw resides in the ext/intl/locale/locale_methods.c file and represents a critical security issue that can be exploited remotely to cause system instability or potentially more severe consequences. The vulnerability stems from improper input validation when processing HTTP Accept-Language headers, creating a pathway for malicious actors to manipulate the underlying ICU (International Components for Unicode) library functions.
The technical root cause of this vulnerability lies in the function's failure to properly restrict the length of arguments passed to the ICU uloc_acceptLanguageFromHTTP function. When a remote attacker submits a specially crafted HTTP request containing an excessively long Accept-Language header, the PHP application fails to validate the input length before passing it to the ICU library. This lack of input sanitization allows for an out-of-bounds read condition where the ICU function attempts to access memory locations beyond the allocated buffer, potentially leading to application crashes or undefined behavior. The vulnerability manifests as a denial of service condition, but research suggests it could also enable more sophisticated attacks depending on the system configuration and memory layout.
From an operational perspective, this vulnerability poses significant risks to web applications that rely on PHP's internationalization features and accept user-provided HTTP headers for locale detection. Attackers can exploit this weakness by crafting malicious HTTP requests with extraordinarily long Accept-Language values, causing the PHP process to crash or behave unpredictably. The impact extends beyond simple service disruption as the vulnerability could potentially be leveraged for information disclosure or other memory corruption attacks, particularly when combined with other vulnerabilities in the application stack. Organizations running affected PHP versions are particularly vulnerable in environments where the intl extension is enabled and used for language negotiation.
The mitigation strategy for CVE-2016-6294 requires immediate patching of affected PHP installations to versions that include the proper input validation fixes. System administrators should upgrade to PHP 5.5.38, 5.6.24, or 7.0.9, depending on their current version, as these releases contain the necessary code modifications to prevent the improper handling of long argument values. Additionally, implementing input validation at the application level can provide defense-in-depth, ensuring that HTTP headers are truncated or rejected if they exceed reasonable length thresholds. Organizations should also consider monitoring for unusual patterns in HTTP Accept-Language headers and implementing rate limiting mechanisms to prevent abuse of this vulnerability. This vulnerability aligns with CWE-129, which addresses improper validation of length of input buffers, and can be categorized under ATT&CK technique T1499.004 for network denial of service attacks, emphasizing the need for robust input validation and proper resource management in web application frameworks.