CVE-2012-1176 in PyFriBidi
Summary
by MITRE
Buffer overflow in the fribidi_utf8_to_unicode function in PyFriBidi before 0.11.0 allows remote attackers to cause a denial of service (application crash) via a 4-byte utf-8 sequence.
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Analysis
by VulDB Data Team • 12/12/2021
The vulnerability identified as CVE-2012-1176 represents a critical buffer overflow flaw within the PyFriBidi library version 0.10.0 and earlier. This issue resides in the fribidi_utf8_to_unicode function which serves as a crucial component for handling Unicode text processing in applications that utilize bidirectional text rendering. The flaw specifically manifests when processing 4-byte utf-8 sequences, which are valid Unicode characters that require proper handling within the conversion process. This vulnerability falls under the Common Weakness Enumeration category CWE-121, which describes stack-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations.
The technical execution of this vulnerability occurs when an attacker crafts a malicious 4-byte utf-8 sequence that exceeds the allocated buffer space within the fribidi_utf8_to_unicode function. The function fails to properly validate the length of incoming utf-8 sequences before attempting to process them, leading to memory corruption that ultimately results in application termination. This type of buffer overflow creates a denial of service condition where legitimate users cannot access the affected application or service. The vulnerability is particularly concerning because it operates at the text processing layer, making it accessible through various attack vectors including web applications, email clients, and any system that processes user-provided text input containing utf-8 encoded characters.
From an operational perspective, this vulnerability presents significant risk to systems that rely on bidirectional text rendering capabilities, particularly those handling internationalized content or multilingual text processing. The impact extends beyond simple application crashes to potentially disrupt critical services where text processing is fundamental to functionality. Attackers can exploit this vulnerability by sending specially crafted utf-8 sequences through input fields, file uploads, or network communications that trigger the vulnerable function. The exploit requires minimal privileges and can be executed remotely, making it particularly dangerous in web-based environments where user input is common. This vulnerability aligns with ATT&CK technique T1203, which involves exploiting input validation flaws to cause system instability.
Mitigation strategies for CVE-2012-1176 focus primarily on upgrading to PyFriBidi version 0.11.0 or later, which contains the necessary fixes to properly handle utf-8 sequence validation and buffer boundaries. Organizations should also implement input sanitization measures at application layers that process utf-8 text to provide additional defense-in-depth. The fix typically involves adding proper bounds checking and length validation before buffer operations, ensuring that the function properly validates the size of incoming utf-8 sequences before attempting conversion. Security teams should conduct comprehensive testing to verify that the upgrade resolves the issue without introducing regressions in text processing functionality. Additionally, monitoring for unusual text processing patterns or application crashes may help detect exploitation attempts, while implementing web application firewalls can provide additional protection against malformed utf-8 sequences reaching vulnerable applications.