CVE-2019-8904 in libmagic
Summary
by MITRE
do_bid_note in readelf.c in libmagic.a in file 5.35 has a stack-based buffer over-read, related to file_printf and file_vprintf.
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Analysis
by VulDB Data Team • 07/11/2023
The vulnerability identified as CVE-2019-8904 represents a critical stack-based buffer over-read flaw within the file command version 5.35, specifically within the libmagic.a library component. This issue manifests in the do_bid_note function located in readelf.c, where improper bounds checking allows for memory access beyond allocated buffer boundaries. The vulnerability is particularly concerning as it occurs during the processing of ELF (Executable and Linkable Format) files, which are fundamental to Unix-like operating systems and are commonly encountered in various security contexts. The flaw is directly related to the file_printf and file_vprintf functions, which are responsible for formatting and outputting file type information, making this vulnerability exploitable during routine file type detection operations.
The technical implementation of this vulnerability stems from inadequate input validation within the ELF parsing logic of the file command. When processing certain malformed or specially crafted ELF files, the do_bid_note function fails to properly constrain buffer access during string formatting operations. This allows an attacker to potentially read data from adjacent memory locations, which could include sensitive information such as stack canaries, return addresses, or other critical program data. The buffer over-read occurs because the function does not properly validate the length of data being processed against the allocated buffer size, creating a scenario where memory beyond the intended boundaries is accessed. This type of vulnerability falls under CWE-121 Stack-based Buffer Overflow, which is classified as a high-severity issue due to its potential for information disclosure and exploitation.
The operational impact of CVE-2019-8904 extends beyond simple information disclosure, as it can be leveraged in more sophisticated attack scenarios within the context of the ATT&CK framework. When an attacker can trigger this vulnerability through file type detection operations, they may gain insights into memory layout that could aid in bypassing security mechanisms such as stack canaries, ASLR (Address Space Layout Randomization), or DEP (Data Execution Prevention). The vulnerability is particularly dangerous in environments where the file command is used for automated file analysis, such as in security scanning tools, malware analysis systems, or network traffic inspection. During normal operation, this vulnerability could be exploited by crafting malicious ELF files that, when processed by the file command, trigger the buffer over-read condition and potentially expose sensitive memory contents to the attacker.
Mitigation strategies for CVE-2019-8904 should focus on both immediate patching and operational security measures. The most effective solution involves updating to file command version 5.36 or later, where the buffer over-read has been corrected through proper bounds checking and input validation. Organizations should also implement defensive programming practices such as using memory-safe programming languages or compilers with stack protection features like stack canaries and address sanitizers. Additionally, security teams should consider implementing network-based detection mechanisms that monitor for suspicious file processing activities, particularly in environments where automated file analysis is performed. The vulnerability demonstrates the importance of proper input validation in security-critical applications and underscores the need for comprehensive testing of file format parsers against malformed inputs, aligning with security best practices outlined in NIST SP 800-160 and ISO/IEC 27001 standards for secure software development.