Source: cve@mitre.org
An issue was discovered in Foxit Reader before 10.1.1 (and before 4.1.1 on macOS) and PhantomPDF before 9.7.5 and 10.x before 10.1.1 (and before 4.1.1 on macOS). An attacker can spoof a certified PDF document via an Evil Annotation Attack because the products fail to consider a null value for a Subtype entry of the Annotation dictionary, in an incremental update.
Foxit Reader and PhantomPDF are vulnerable to a certificate spoofing attack that allows attackers to create seemingly legitimate, signed PDF documents. This vulnerability, stemming from a failure to properly validate annotation subtypes in incremental updates, could lead to malicious code execution and data theft by deceiving users into trusting compromised documents.
Step 1: Payload Creation: The attacker crafts a legitimate-looking PDF document, potentially with a valid digital signature to increase trust.
Step 2: Incremental Update Crafting: The attacker creates an incremental update to the PDF. This update adds an Annotation dictionary.
Step 3: Null Subtype Injection: Within the Annotation dictionary of the incremental update, the attacker sets the Subtype entry to a null value.
Step 4: Malicious Annotation Content: The attacker includes malicious content within the annotation, such as JavaScript code or links to a malicious website.
Step 5: Document Delivery: The attacker delivers the modified PDF document to the victim, potentially through email, a website, or other means.
Step 6: Reader Processing: When the victim opens the modified PDF in a vulnerable version of Foxit Reader or PhantomPDF, the software processes the incremental update.
Step 7: Exploitation: Due to the lack of validation of the null Subtype, the malicious annotation is processed. This can lead to the execution of JavaScript, redirection to a malicious website, or other undesirable actions, effectively spoofing the document's integrity and potentially leading to further exploitation.
The vulnerability lies in the improper handling of the Subtype entry within the Annotation dictionary of a PDF document during incremental updates. Specifically, the software fails to validate if the Subtype entry is null. An attacker can craft a malicious PDF with an incremental update that includes an Annotation dictionary with a null Subtype. Because the software doesn't properly check this, it proceeds to process the annotation, potentially leading to unexpected behavior. This could involve the execution of JavaScript, the display of misleading content, or the redirection to malicious websites. The root cause is a logic error in the parsing and validation of PDF annotation data, specifically the lack of a check for a null Subtype value. This allows for the injection of malicious annotations, bypassing security checks that rely on the integrity of the document's structure and digital signatures. The vulnerability leverages the trust users place in digitally signed PDFs.
While no specific APTs are definitively linked, the ease of exploitation and the potential for high impact make this a desirable target for various threat actors. This type of vulnerability is often leveraged by actors seeking to distribute malware or conduct phishing campaigns. CISA KEV: Not listed.
Monitor network traffic for suspicious PDF downloads or access attempts.
Analyze PDF documents for unusual annotation structures, especially those with null or unexpected Subtype values within the Annotation dictionary.
Implement file integrity monitoring to detect changes to PDF files.
Use a Security Information and Event Management (SIEM) system to correlate events and identify suspicious activity related to PDF documents.
Examine PDF metadata for inconsistencies or anomalies, such as unexpected digital signatures or modifications.
Employ endpoint detection and response (EDR) solutions to monitor for malicious activity, such as JavaScript execution or network connections initiated by PDF readers.
Update Foxit Reader and PhantomPDF to the latest versions (10.1.1 or later for Foxit Reader and 9.7.5 or 10.1.1 or later for PhantomPDF).
Educate users about the risks of opening PDF documents from untrusted sources.
Implement a robust email security gateway to scan for malicious PDF attachments.
Configure PDF readers to disable JavaScript execution by default, or to prompt users before executing JavaScript.
Use a PDF security tool to validate PDF documents and detect potentially malicious content.
Regularly scan systems for vulnerable versions of Foxit Reader and PhantomPDF.
Implement a defense-in-depth strategy, including network segmentation and intrusion detection/prevention systems.