CVE-2018-20452 in libxls
Summary
by MITRE
The read_MSAT_body function in ole.c in libxls 1.4.0 has an invalid free that allows attackers to cause a denial of service (application crash) or possibly have unspecified other impact via a crafted file, because of inconsistent memory management (new versus free) in ole2_read_header in ole.c.
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Analysis
by VulDB Data Team • 06/22/2023
The vulnerability identified as CVE-2018-20452 resides within the libxls library version 1.4.0, specifically in the read_MSAT_body function located in the ole.c file. This issue represents a critical memory management flaw that can be exploited to trigger application instability or potentially more severe consequences through the manipulation of specially crafted file inputs. The vulnerability stems from inconsistent handling of memory allocation and deallocation operations, creating a scenario where the application attempts to free memory that was not allocated through the same memory management pathway.
The technical root cause of this vulnerability lies in the improper interaction between memory allocation and deallocation functions within the ole2_read_header function. When processing structured storage files, particularly those following the OLE2 format, the library employs different memory management approaches that create a mismatch between allocation and deallocation operations. This inconsistency creates a condition where a free operation is performed on memory that was allocated through a different mechanism, leading to undefined behavior in the application's memory management system. The flaw manifests when the library processes malformed or crafted input files that trigger the specific code path involving the read_MSAT_body function.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially enable more sophisticated attack vectors. An attacker can craft malicious files that, when processed by applications relying on libxls for spreadsheet file handling, will cause the target application to crash or behave unpredictably. This vulnerability affects any application that utilizes libxls version 1.4.0 for reading excel or ole2 formatted files, including but not limited to office automation tools, data processing applications, and file analysis utilities. The instability can be leveraged to disrupt services or potentially escalate to more severe consequences depending on the execution context of the vulnerable application.
This vulnerability aligns with CWE-415 which describes double free conditions and CWE-416 which covers use after free errors, both of which are manifestations of improper memory management. From an attack framework perspective, this issue maps to the execution phase of the ATT&CK methodology where adversaries can leverage memory corruption vulnerabilities to cause system instability or gain unauthorized access. The vulnerability demonstrates poor defensive programming practices and highlights the importance of maintaining consistent memory management protocols throughout software components. Organizations should prioritize immediate patching of affected systems and implement input validation measures to prevent processing of untrusted spreadsheet files until proper updates are deployed.
The remediation strategy requires updating to a patched version of libxls where the memory management inconsistency has been resolved through proper allocation and deallocation matching. Security teams should conduct comprehensive vulnerability assessments to identify all systems utilizing the affected library version and ensure proper patch deployment across all environments. Additionally, implementing strict input validation and sanitization measures for spreadsheet file processing can provide additional defense-in-depth layers against exploitation attempts. The vulnerability underscores the critical importance of thorough memory management review processes in security-critical libraries and the need for comprehensive testing of edge cases in file processing components.