CVE-2026-91802 in PDF Editor
Summary
by MITRE • 09/23/2026
A heap-based out-of-bounds write vulnerability exists in Foxit PDF Editor/Reader’s WebP image decoding due to improper handling of bitmap stride and target buffer formats. Successful exploitation could result in an application crash.
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Analysis
by VulDB Data Team • 09/23/2026
The identified security flaw resides within the core image processing subsystem of Foxit PDF Editor and Reader, specifically affecting the module responsible for decoding WebP format images. This vulnerability is classified as a heap-based out-of-bounds write, which corresponds to CWE-787 in the Common Weakness Enumeration taxonomy. The root cause stems from an improper validation mechanism regarding bitmap stride values and target buffer formats during the image rendering pipeline. When the application processes a maliciously crafted WebP file, it fails to adequately verify that the calculated memory allocation size matches the actual data being written by the decoder. This discrepancy allows an attacker to write data beyond the boundaries of the allocated heap memory region.
From a technical perspective, the vulnerability exploits the lack of rigorous bounds checking when mapping image dimensions and stride parameters to internal buffer structures. In standard image processing workflows, the stride represents the number of bytes per row in the bitmap, which often includes padding for alignment purposes. If an attacker manipulates these values within the WebP container metadata or encoded stream data, they can trick the decoder into writing pixel data or structural headers into adjacent memory locations on the heap. This overwriting behavior corrupts critical data structures such as linked list pointers, object vtables, or other control flow elements stored in nearby heap chunks. The immediate operational impact of this flaw is typically a denial of service manifested by an application crash due to segmentation faults or access violations when the corrupted memory is subsequently accessed.
While the primary observed effect is an application crash, heap-based out-of-bounds writes are historically significant vectors for arbitrary code execution if specific exploitation techniques such as heap spraying or use-after-free conditions can be combined with this flaw. An attacker could potentially leverage this instability to overwrite function pointers or return addresses, thereby gaining control over program execution flow. This aligns with ATT&CK technique T1203, which covers Exploitation for Client Execution, particularly in the context of malicious document delivery via PDF files containing embedded WebP assets. The severity is further compounded by the widespread use of Foxit software across enterprise environments where users frequently open documents from untrusted sources.
Mitigation strategies should prioritize immediate patching to the latest version of Foxit PDF Editor and Reader provided by the vendor, as these updates typically include hardened input validation routines for image decoding libraries. Organizations must enforce strict application whitelisting policies to prevent unauthorized execution of potentially compromised binaries. Additionally, implementing network-level controls such as deep packet inspection or sandboxed document analysis can help detect and block malicious WebP payloads before they reach end-user workstations. Users should be educated on the risks associated with opening PDF files from unknown origins, particularly those containing embedded multimedia content that triggers complex rendering engines. Regular vulnerability scanning and patch management cycles are essential to maintain a secure posture against such memory corruption vulnerabilities.