CVE-2019-20835 in Foxit
Summary
by MITRE
An issue was discovered in Foxit Reader and PhantomPDF before 9.5. It has homograph mishandling.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 10/22/2020
The vulnerability identified as CVE-2019-20835 represents a critical security flaw in Foxit Reader and PhantomPDF software versions prior to 9.5, specifically addressing homograph mishandling issues that can lead to sophisticated phishing attacks and credential theft. This vulnerability falls under the broader category of Unicode homograph attacks where malicious actors exploit the visual similarity of characters from different scripts to deceive users into believing they are interacting with legitimate systems. The flaw manifests when the software fails to properly validate and display Unicode characters that appear visually identical or similar across different character sets, creating opportunities for attackers to craft deceptive URLs, file names, or document titles that masquerade as trusted entities.
The technical implementation of this vulnerability stems from inadequate input validation and character encoding handling within the PDF rendering and parsing components of these applications. When processing PDF documents containing Unicode characters, the affected software does not sufficiently sanitize or normalize character sequences that could represent homograph attacks. This failure allows attackers to embed malicious Unicode characters that visually resemble legitimate domain names, file extensions, or application interfaces, effectively bypassing user security awareness and traditional defense mechanisms. The vulnerability is particularly dangerous because it operates at the user interface level where visual deception is most effective, making it difficult for users to distinguish between legitimate and malicious content through visual inspection alone.
The operational impact of this vulnerability extends beyond simple phishing attempts to encompass broader security risks including credential harvesting, malware delivery, and unauthorized access to sensitive information. Attackers can exploit this flaw by crafting PDF documents that appear to originate from trusted sources such as banks, government agencies, or corporate networks, while actually directing users to malicious websites or triggering unwanted actions within the PDF viewer. The vulnerability affects the core functionality of both Foxit Reader and PhantomPDF, meaning that any user opening potentially malicious PDF documents could be compromised, regardless of their security awareness or network protection measures. This makes the attack surface particularly broad and difficult to defend against through traditional user education alone.
Organizations and users should immediately update to Foxit Reader and PhantomPDF version 9.5 or later to remediate this vulnerability, as no effective workarounds exist for the underlying character handling flaws. The mitigation strategy should also include enhanced network monitoring to detect suspicious character sequences in URLs and file names, along with regular security assessments of PDF handling capabilities within the organization. From a cybersecurity framework perspective, this vulnerability aligns with CWE-1004 which addresses insecure default configurations and CWE-770 which covers excessive resource consumption through improper input validation. The attack pattern corresponds to ATT&CK technique T1566 which involves phishing through social engineering, and T1059 which encompasses command and scripting interpreter usage. Security professionals should implement comprehensive endpoint protection measures including real-time scanning of PDF documents and enhanced user behavior analytics to detect potential exploitation attempts, while also considering the broader implications of Unicode handling across all document processing applications within their environment.