CVE-2007-4771 in International Components for Unicode
Summary
by MITRE
Heap-based buffer overflow in the doInterval function in regexcmp.cpp in libicu in International Components for Unicode (ICU) 3.8.1 and earlier allows context-dependent attackers to cause a denial of service (memory consumption) and possibly have unspecified other impact via a regular expression that writes a large amount of data to the backtracking stack. NOTE: some of these details are obtained from third party information.
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Analysis
by VulDB Data Team • 08/04/2019
The vulnerability identified as CVE-2007-4771 represents a critical heap-based buffer overflow within the International Components for Unicode (ICU) library version 3.8.1 and earlier. This flaw exists in the doInterval function located in the regexcmp.cpp file, which forms part of the core regular expression processing capabilities of the ICU library. The issue manifests when processing certain regular expressions that trigger excessive memory consumption during backtracking operations, creating a scenario where malicious input can cause system instability and resource exhaustion.
The technical implementation of this vulnerability stems from inadequate bounds checking within the regular expression compiler's backtracking mechanism. When the doInterval function encounters a regular expression pattern that requires extensive backtracking, it allocates memory on the heap to maintain the backtracking stack. However, the function fails to properly validate the amount of data that can be written to this stack, allowing attackers to craft patterns that cause exponential memory growth. This behavior aligns with CWE-121, heap-based buffer overflow, and specifically relates to improper input validation in regular expression processing. The vulnerability operates in a context-dependent manner, meaning that the attack vector requires specific conditions to be met for exploitation to occur.
The operational impact of CVE-2007-4771 extends beyond simple denial of service to potentially encompass more severe consequences including system instability and resource exhaustion attacks. Attackers can leverage this vulnerability to consume excessive memory resources, leading to system performance degradation or complete system crashes. The memory consumption pattern typically follows a predictable but potentially exponential growth curve as the backtracking stack expands with each recursive pattern match attempt. This type of vulnerability falls under the ATT&CK technique T1499.004, which involves network denial of service attacks, and can be classified as a resource exhaustion attack that targets application memory management. The vulnerability is particularly dangerous in environments where ICU is used for input validation or text processing, as it can be triggered through user-supplied input.
Mitigation strategies for CVE-2007-4771 require immediate attention through patching the affected ICU library to version 3.9.0 or later, where the buffer overflow has been addressed through improved bounds checking and stack management. Organizations should implement input validation measures that limit the complexity and length of regular expressions processed by applications using ICU, particularly in scenarios involving user input. Network-level protections such as rate limiting and input sanitization can help reduce the attack surface, while application-level monitoring should track memory consumption patterns that might indicate exploitation attempts. Additionally, implementing proper error handling and graceful degradation mechanisms can help prevent complete system failures when memory exhaustion occurs, aligning with defensive techniques outlined in MITRE ATT&CK framework under the application security domain.