CVE-2021-21822: 
Foxit PDF Reader vulnerability analysis and mitigation

CVE-2021-21822 is a use-after-free vulnerability discovered in Foxit Software's PDF Reader version 10.1.3.37598. The vulnerability was disclosed on April 26, 2021, and patched on May 6, 2021. The issue affects the JavaScript engine of the PDF reader, specifically in how it handles FileAttachment annotations (Talos Report).

The vulnerability exists in the JavaScript engine's handling of certain annotation types. When a specially crafted PDF document triggers a page change and creates a FileAttachment annotation, a race condition occurs between the page close handler and annotation creation. The page close handler destroys the annotation, freeing its memory, but the annotation creation code continues execution with the freed memory, leading to memory corruption. The vulnerability has a CVSS v3.1 score of 8.8 (HIGH) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H (NVD).

If successfully exploited, this vulnerability can lead to arbitrary code execution on the affected system. The vulnerability is particularly concerning as it affects one of the most popular PDF readers with a large user base. An attacker could execute malicious code with the same privileges as the user running the PDF reader (Talos Report).

Foxit Software released a patch for this vulnerability in version 10.1.4.37651. However, it was later discovered that the initial fix was incomplete, leading to the assignment of a new CVE (CVE-2021-21870) for the same vulnerability pattern in the patched version. Users are advised to update to the latest version of Foxit Reader that includes complete fixes for these vulnerabilities (Talos Report).