CVE-2010-4156 in Libmbfl
Summary
by MITRE
The mb_strcut function in Libmbfl 1.1.0, as used in PHP 5.3.x through 5.3.3, allows context-dependent attackers to obtain potentially sensitive information via a large value of the third parameter (aka the length parameter).
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Analysis
by VulDB Data Team • 01/04/2025
The vulnerability identified as CVE-2010-4156 represents a sensitive information disclosure flaw within the mb_strcut function implementation in Libmbfl version 1.1.0, which was integrated into PHP versions 5.3.x through 5.3.3. This issue stems from improper handling of input validation within the multibyte string cutting functionality, creating a potential avenue for attackers to extract unintended memory contents. The vulnerability manifests when the third parameter, representing the length of characters to extract, is set to an excessively large value, allowing the function to read beyond intended boundaries and potentially expose sensitive data from adjacent memory locations.
The technical root cause of this vulnerability lies in the insufficient bounds checking within the mb_strcut implementation, which fails to properly validate the length parameter against the actual available string buffer. When an attacker provides an oversized length value, the function does not adequately verify that the requested extraction range remains within the confines of the source string, leading to buffer over-read conditions. This behavior aligns with CWE-125, which describes out-of-bounds read vulnerabilities, and demonstrates how improper input validation can result in information disclosure. The flaw operates within the context of multibyte character processing where the function's handling of character boundaries becomes critical to memory safety.
The operational impact of this vulnerability extends beyond simple information disclosure, as the sensitive data potentially exposed could include cryptographic keys, session tokens, or other confidential information stored in adjacent memory segments. Attackers can leverage this weakness by crafting malicious input parameters that trigger the buffer over-read condition, thereby gaining access to data that should remain protected. This type of vulnerability falls under the ATT&CK technique T1005, which covers data from local system, and represents a significant risk to applications processing user input through multibyte string functions. The vulnerability affects web applications where user-supplied data is processed through PHP's mb_strcut function, particularly those handling international text or character encodings.
Mitigation strategies for CVE-2010-4156 require immediate patching of affected PHP installations to versions that contain corrected implementations of the mb_strcut function. Organizations should also implement proper input validation mechanisms that sanitize all parameters passed to multibyte string functions, ensuring that length parameters remain within reasonable bounds. Additional defensive measures include monitoring application logs for unusual parameter patterns and implementing runtime protections such as address space layout randomization and stack canaries. The vulnerability highlights the importance of comprehensive input validation in security-critical functions and serves as a reminder of the risks associated with insufficient bounds checking in memory-intensive operations, particularly those involving character encoding and multibyte string processing.