CVE-2026-91752 in libextractor
Summary
by MITRE • 09/15/2026
GNU libextractor before 1.15 contains a stack-based buffer overflow vulnerability in the process_star_office function that sizes a variable-length stack array from attacker-controlled OLE2 stream data. Attackers can craft malicious StarOffice documents that allocate up to 4 MB on the stack, causing stack overflow and crashing any application extracting metadata from the document.
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Analysis
by VulDB Data Team • 09/15/2026
The vulnerability identified in GNU libextractor prior to version 1.15 represents a critical memory safety failure within the library's handling of OLE2 structured storage files, specifically those associated with StarOffice documents. This flaw is located within the process_star_office function, which is responsible for parsing and extracting metadata from these complex file formats. The core technical issue stems from an improper validation of input data lengths before allocating stack memory. Specifically, the application sizes a variable-length array on the call stack based directly on values extracted from attacker-controlled OLE2 stream headers without sufficient bounds checking or sanity verification against available system resources. This design oversight allows malicious actors to inject crafted file metadata that specifies extremely large dimensions for internal buffers, leading to an immediate and uncontrolled allocation of memory space on the limited stack region.
From a technical perspective, this is classified as CWE-121: Stack-based Buffer Overflow. The vulnerability exploits the fact that modern operating systems allocate significantly less memory to the process stack compared to heap memory, typically ranging from one megabyte to eight megabytes depending on system configuration and thread settings. By forcing the application to attempt an allocation of up to four megabytes within this constrained space, the exploit triggers a stack overflow condition almost immediately upon processing the malicious document. Unlike heap-based overflows which may allow for more complex exploitation chains involving arbitrary code execution through sophisticated memory corruption techniques, stack-based overflows in this context primarily result in immediate control flow disruption. The excessive allocation causes the program counter to be overwritten or corrupted as it attempts to return from the function call, leading inevitably to a segmentation fault and application crash.
The operational impact of this vulnerability is predominantly focused on availability rather than confidentiality or integrity for most end-users. Since GNU libextractor is often used by other applications such as file managers, email clients, and document viewers to preview metadata before opening files, the exploitation results in Denial of Service conditions. Any application integrating this library will terminate unexpectedly when a user attempts to view properties or extract information from a specially crafted StarOffice document. This can disrupt workflows that rely on automated batch processing of documents or cause instability in desktop environments where file previews are generated dynamically as users browse directories. While the primary outcome is a crash, the underlying memory corruption mechanism theoretically poses risks if combined with other vulnerabilities or specific compiler protections being disabled, though the immediate threat vector is stability degradation.
This vulnerability aligns with MITRE ATT&CK technique T1496: Resource Hijacking under the broader category of Impact, specifically manifesting as Denial of Service through resource exhaustion. It also reflects CWE-787: Out-of-bounds Write if considering the potential for overwriting adjacent stack variables during the overflow process, although the primary manifestation is allocation failure leading to crash. The lack of input validation on external data sources such as OLE2 streams highlights a common pattern in legacy parsing libraries where performance optimizations bypassed necessary security checks against malformed inputs.
Mitigation strategies primarily involve upgrading GNU libextractor to version 1.15 or later, which includes patches for this specific buffer overflow issue by implementing proper size validation and safe allocation practices. For organizations unable to upgrade immediately due to dependency constraints, defensive measures should include deploying file inspection gateways that sanitize incoming documents before they reach systems running the vulnerable library. Additionally, enabling stack protection mechanisms such as Stack Canaries (GCC -fstack-protector) can help detect and abort execution upon detecting buffer overflow attempts, although this does not prevent the initial allocation failure or crash in all cases. Security teams should also audit applications that integrate libextractor to ensure they handle exceptions gracefully during metadata extraction processes, preventing single-point failures from cascading into broader system instability.