Description

A heap-based out-of-bounds read vulnerability exists in Foxit PDF Editor/Reader’s handling of wide strings in embedded PDF JavaScript. Insufficient validation of string-deletion ranges can cause an integer underflow, resulting in an out-of-bounds read and application crash.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "6.1",
  "pubDate": "2026-09-23T08:17:14.010Z",
  "pubdate": "2026-09-23T08:17:14.010Z",
  "executiveSummary": "A heap-based out-of-bounds (OOB) read vulnerability has been identified in Foxit PDF Editor and Reader. The flaw resides within the application's processing of wide strings during embedded PDF JavaScript execution. By manipulating string-deletion ranges, an attacker can trigger an integer underflow, leading to unauthorized memory access.\nThe vulnerability allows for an out-of-bounds memory read, which typically results in an application crash (Denial of Service). In more advanced exploitation scenarios, such memory corruption primitives can potentially be leveraged to bypass security controls like Address Space Layout Randomization (ASLR) or to facilitate arbitrary code execution by leaking sensitive memory contents.\nThe vulnerability affects Foxit PDF Editor and Reader components responsible for parsing JavaScript objects within PDF documents. Exploitation requires the victim to open a maliciously crafted PDF file containing an embedded JavaScript payload, necessitating user interaction. The risk is significant, as successful exploitation could lead to information disclosure or the destabilization of the application process. Organizations and users are advised to remain vigilant regarding document sources and apply relevant security updates as they become available from the vendor.",
  "technicalDetails": "The root cause of this vulnerability is improper bounds validation during the management of wide strings within the Foxit PDF JavaScript engine. When the engine processes JavaScript commands that modify or delete segments of wide string buffers, the logic responsible for calculating the resulting string length and memory boundaries fails to account for specific range edge cases. This failure creates an opportunity for an integer underflow condition.\nSpecifically, when an attacker provides a crafted delete operation via JavaScript, the calculation of the start and end offsets for the deletion range can wrap around due to insufficient integer signedness or bounds checking. This underflow causes the engine to calculate an invalid, excessively large length for the remaining string buffer. When the application subsequently attempts to perform a read operation or copy from this corrupted heap buffer, it accesses memory locations beyond the intended bounds of the allocated object.\nThe attack flow commences with the delivery of a malicious PDF file containing an embedded JavaScript snippet. Upon the application parsing the PDF and executing the script, the engine initializes the wide string object. The attacker then triggers the vulnerable function call by invoking a string manipulation method (such as .slice(), .substring(), or similar string-processing methods) with carefully calculated arguments designed to trigger the underflow. The heap-based OOB read occurs as the engine attempts to process the resulting buffer, which now points to a memory offset outside of the legitimate heap chunk.\nFrom a technical perspective, this primitive allows an attacker to read adjacent data residing in the heap. Because JavaScript objects in PDF readers often occupy contiguous memory addresses, this OOB read can be used to leak pointers, object metadata, or other sensitive information residing on the heap. This leakage is a critical precursor to bypassing exploit mitigations; for instance, leaking a function pointer can allow an attacker to defeat ASLR. Once the memory layout is mapped, the attacker may pivot to a more severe vulnerability—such as a heap overflow or type confusion—to achieve reliable arbitrary code execution.\nThe vulnerability is exposed through the PDF JavaScript interface, meaning the attacker does not need prior authentication; however, the exploit is contingent upon user interaction (opening a file). The flaw demonstrates a lack of robust input sanitization in the underlying C++ components that interface with the JavaScript engine, highlighting a need for stricter boundary enforcement during heap-based string operations."
}