CVE-2018-18585 in libmspack
Summary
by MITRE
chmd_read_headers in mspack/chmd.c in libmspack before 0.8alpha accepts a filename that has '\0' as its first or second character (such as the "/\0" name).
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Analysis
by VulDB Data Team • 05/30/2023
The vulnerability identified as CVE-2018-18585 resides within the libmspack library, specifically in the chmd_read_headers function located in mspack/chmd.c. This flaw represents a classic input validation issue that can lead to unpredictable behavior when processing malformed input data. The vulnerability manifests when the library encounters a filename where the first or second character is a null byte character, represented as ''. This particular condition allows for the processing of filenames with null terminators at critical positions, creating an opportunity for unexpected program behavior. The issue affects libmspack versions prior to 0.8alpha, indicating this was a known problem that required a specific version update to resolve. The vulnerability stems from inadequate validation of input parameters, particularly filename strings that should be strictly validated for proper formatting and character sequences.
The technical implementation of this vulnerability involves the function's failure to properly sanitize or validate filename inputs before processing them. When a filename begins with a null byte character, the function does not adequately handle this edge case, potentially leading to memory access violations or buffer overflows. The null byte character serves as a string terminator in many programming languages and systems, so its unexpected appearance at the beginning of a filename can cause parsing functions to misinterpret the data structure. This flaw can be exploited by an attacker who crafts malicious filenames with null bytes, potentially causing the application to behave unexpectedly or crash. The vulnerability operates at the boundary condition level where standard input validation fails to account for null byte characters at the start of string inputs, creating a pathway for abnormal execution flow.
The operational impact of CVE-2018-18585 extends beyond simple application instability to potential security implications within systems that rely on libmspack for processing Microsoft help files or compressed content. When applications using this library process maliciously crafted files, the vulnerability can result in denial of service conditions, application crashes, or potentially more severe consequences depending on the context in which the library is used. The vulnerability affects systems that handle compressed help files, documentation formats, or any content that utilizes the chm file format, which is commonly found in Microsoft help systems and documentation. Attackers could exploit this by providing specially crafted filenames that trigger the vulnerable code path, potentially causing system instability or resource exhaustion. The impact is particularly concerning in environments where automated processing of user-provided content occurs, as it could enable remote exploitation or escalation of privileges.
Mitigation strategies for this vulnerability center on upgrading to libmspack version 0.8alpha or later, which contains the necessary fixes to properly validate filename inputs. System administrators should prioritize patching affected systems and applications that depend on this library to prevent exploitation. Additionally, input validation should be implemented at the application level to sanitize filename inputs before they reach the vulnerable library functions. The fix typically involves adding proper bounds checking and null byte validation to prevent the processing of filenames with null characters at critical positions. Organizations should also consider implementing proper monitoring and logging for unusual filename patterns that might indicate attempted exploitation. This vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and could be categorized under ATT&CK technique T1203 for exploitation of input validation flaws. The remediation process requires careful testing to ensure that legitimate functionality is not broken while addressing the specific edge case that triggers this vulnerability.