CVE-2011-4599 in iOS
Summary
by MITRE
Stack-based buffer overflow in the _canonicalize function in common/uloc.c in International Components for Unicode (ICU) before 49.1 allows remote attackers to execute arbitrary code via a crafted locale ID that is not properly handled during variant canonicalization.
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Analysis
by VulDB Data Team • 04/13/2021
The vulnerability identified as CVE-2011-4599 represents a critical stack-based buffer overflow within the International Components for Unicode (ICU) library, specifically affecting versions prior to 49.1. This flaw resides in the _canonicalize function located in the common/uloc.c file, which is responsible for handling locale identifier canonicalization. The issue arises when processing crafted locale IDs that undergo variant canonicalization, creating a condition where attacker-controlled input can overflow stack buffers and potentially lead to arbitrary code execution. The ICU library serves as a fundamental component for internationalization and localization in numerous software applications, making this vulnerability particularly dangerous as it can affect a wide range of systems and applications that depend on proper locale handling.
The technical exploitation of this vulnerability occurs through a stack-based buffer overflow condition that manifests during the canonicalization process of locale identifiers. When the _canonicalize function processes a specially crafted locale ID containing malicious input, the function fails to properly validate the length of variant components within the locale identifier. This insufficient input validation allows an attacker to provide input that exceeds the allocated buffer space on the stack, causing a buffer overflow that can overwrite adjacent memory locations including return addresses and control data. The vulnerability falls under CWE-121, which specifically addresses stack-based buffer overflow conditions, and represents a classic example of improper input validation leading to memory corruption. The attack vector is remote, meaning that an attacker can trigger the vulnerability through network-based input without requiring local system access.
The operational impact of CVE-2011-4599 extends far beyond the immediate technical flaw, as the ICU library is widely integrated into numerous software platforms and applications. This includes major operating systems, web browsers, enterprise applications, and middleware components that rely on proper internationalization support. When exploited, the buffer overflow can lead to complete system compromise, allowing attackers to execute arbitrary code with the privileges of the affected application. The vulnerability affects systems where locale identifiers are processed from untrusted sources, such as web applications parsing user input, network protocols handling locale information, or any software component that accepts and processes locale identifiers. The potential for remote code execution makes this vulnerability particularly attractive to threat actors seeking to compromise systems at scale, as it requires minimal privileges to exploit and can affect multiple applications simultaneously.
Mitigation strategies for CVE-2011-4599 primarily focus on upgrading to ICU version 49.1 or later, which contains the necessary patches to address the buffer overflow condition. Organizations should conduct comprehensive inventory assessments to identify all systems and applications that utilize ICU libraries, particularly those handling user-provided locale information. The patch implementation requires careful testing to ensure compatibility, as upgrading ICU versions may introduce breaking changes in existing applications. Additional defensive measures include implementing input validation controls at application layers to sanitize locale identifiers before they reach the ICU library functions, employing stack protection mechanisms such as stack canaries, and utilizing address space layout randomization to complicate exploitation attempts. Network segmentation and access controls should be implemented to limit exposure of systems that process untrusted locale data, while monitoring systems should be configured to detect unusual patterns in locale identifier processing that might indicate exploitation attempts. The vulnerability also highlights the importance of keeping third-party libraries updated and implementing proper security testing procedures that include fuzzing and static analysis of internationalization components.