CVE-2026-57251: Foxit PDF Editor DOS Vulnerability

CVE-2026-57251 Overview

CVE-2026-57251 is an out-of-bounds access vulnerability affecting Foxit PDF Editor and Foxit PDF Reader on Microsoft Windows. The flaw resides in the construction process for cloud-like appearance rendering when opening a PDF document. The implementation lacks an upper limit and consistency checks, allowing out-of-bounds access to the underlying array. An attacker who convinces a user to open a crafted PDF can trigger the condition, ultimately crashing the application and potentially compromising confidentiality, integrity, and availability. The vulnerability is classified under [CWE-129] (Improper Validation of Array Index).

Critical Impact
Opening a malicious PDF triggers out-of-bounds array access in Foxit PDF Editor and Reader, crashing the application and risking high-impact compromise on the local host.

Affected Products

Foxit PDF Editor (Windows)
Foxit PDF Reader (Windows)
Microsoft Windows

Discovery Timeline

2026-07-08 - CVE-2026-57251 published to NVD
2026-07-09 - Last updated in NVD database

Technical Details for CVE-2026-57251

Vulnerability Analysis

The vulnerability occurs while Foxit PDF applications parse and render the cloud-like appearance construction used for annotation borders and shapes in PDF documents. During this process, the code builds an array of points or segments describing the visual appearance. Because the implementation fails to enforce an upper bound on the number of elements and does not validate consistency between the declared and actual array sizes, attacker-controlled inputs can drive the index beyond the allocated buffer. The result is out-of-bounds access, producing memory corruption or a read of unmapped memory, and terminating the application. Successful exploitation requires local file interaction, meaning the victim must open the crafted PDF.

Root Cause

The root cause is improper validation of an array index during construction of the cloud-like appearance geometry. The parser accepts a segment or vertex count from the PDF stream without bounding it against the size of the destination array and without cross-checking related fields. This maps directly to [CWE-129], improper validation of array index.

Attack Vector

Exploitation requires the victim to open a specially crafted PDF file locally in Foxit PDF Editor or Foxit PDF Reader. No prior authentication is needed, but user interaction is required. Delivery typically occurs through phishing emails, malicious downloads, or shared document workflows. Once the file is opened, the malformed cloud appearance definition drives the parser into out-of-bounds territory, crashing the process and creating conditions that may impact the confidentiality and integrity of the process memory.

No verified proof-of-concept is publicly available. Refer to the Foxit Security Bulletins for technical detail.

Detection Methods for CVE-2026-57251

Indicators of Compromise

Unexpected crashes of FoxitPDFReader.exe or FoxitPDFEditor.exe shortly after opening a PDF attachment.
Windows Error Reporting (WER) entries referencing access violations in Foxit PDF modules.
PDF files containing anomalously large or malformed annotation appearance streams with cloud border styles.

Detection Strategies

Inspect PDF files at the mail gateway for oversized or malformed annotation appearance dictionaries and cloud border definitions.
Correlate Foxit process crash events with recent file-open activity from email or web download sources.
Hunt for suspicious child process creation or memory anomalies originating from Foxit PDF applications.

Monitoring Recommendations

Enable and forward Windows Application and WER logs to a centralized analytics platform for anomaly detection.
Monitor endpoints for repeated Foxit crashes across multiple users, which may indicate a distribution campaign.
Track PDF file provenance to identify externally sourced documents opened by high-risk users.

How to Mitigate CVE-2026-57251

Immediate Actions Required

Update Foxit PDF Editor and Foxit PDF Reader to the latest version referenced in the Foxit security bulletin.
Restrict opening of PDFs from untrusted email attachments and external sources until patching is complete.
Train users to report unexpected application crashes tied to PDF documents.

Patch Information

Foxit has published guidance in its security bulletins. Review the Foxit Security Bulletins page for fixed versions and apply the update across all Windows endpoints running Foxit PDF Editor or Foxit PDF Reader.

Workarounds

Set an alternative default PDF handler on Windows until patched builds are deployed.
Disable rendering of annotations with cloud border styles where the application configuration permits.
Apply application allowlisting or attachment filtering policies to block PDFs from untrusted senders.

bash

# Configuration example: change the default PDF handler on Windows via registry (per-user)
reg add "HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.pdf\UserChoice" /v ProgId /t REG_SZ /d "MSEdgePDF" /f