CVE-2018-21239 in Foxit
Summary
by MITRE
An issue was discovered in Foxit Reader and PhantomPDF before 9.2. It allows NTLM credential theft via a GoToE or GoToR action.
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Analysis
by VulDB Data Team • 10/22/2020
The vulnerability identified as CVE-2018-21239 represents a critical security flaw in Foxit Reader and PhantomPDF software versions prior to 9.2 that enables unauthorized NTLM credential theft through specific PDF actions. This issue exploits the way these PDF readers handle navigation commands, specifically the GoToE and GoToR actions that are commonly used to create hyperlinks within PDF documents. The flaw allows malicious actors to craft PDF files that, when opened in vulnerable versions, can trigger credential theft mechanisms without user awareness or consent.
The technical implementation of this vulnerability stems from improper handling of Uniform Resource Identifiers within PDF documents. When a PDF contains a GoToE or GoToR action that references a network resource, the vulnerable Foxit software fails to properly validate or sanitize the destination URL before attempting to establish a connection. This oversight creates an attack vector where an attacker can craft a malicious PDF containing a URL that references an attacker-controlled server, potentially capturing NTLM authentication hashes during the connection attempt. The vulnerability specifically affects the NTLM authentication protocol implementation within the PDF reader's network handling capabilities, making it particularly dangerous in enterprise environments where NTLM is commonly used for authentication.
The operational impact of this vulnerability extends beyond simple credential theft, as it can enable broader attack chains within network environments. When NTLM hashes are captured, attackers can potentially perform pass-the-hash attacks, gain unauthorized access to network resources, and escalate privileges within the compromised environment. This vulnerability is particularly concerning in corporate settings where Foxit Reader is commonly used for document sharing and review processes, as it can be exploited through social engineering attacks where users unknowingly open malicious PDF attachments. The attack requires minimal user interaction beyond opening the PDF file, making it highly effective for phishing campaigns and targeted attacks against specific organizations.
Mitigation strategies for CVE-2018-21239 should prioritize immediate software updates to Foxit Reader and PhantomPDF versions 9.2 or later, which contain patches addressing the NTLM credential theft vulnerability. Organizations should also implement network-level protections such as disabling or restricting outbound connections from PDF readers, particularly for network resources that might be exploited in this manner. Security configurations should include monitoring for unusual network activity patterns that might indicate credential theft attempts, and network segmentation can help limit the potential impact if an attacker successfully exploits this vulnerability. The vulnerability aligns with CWE-200, which addresses improper exposure of sensitive information, and maps to ATT&CK technique T1075, related to legitimate credentials usage for persistence and privilege escalation. Additionally, organizations should consider implementing application whitelisting policies that restrict PDF reader execution to known good software versions and establish security awareness training to reduce the risk of users opening malicious PDF files.