CVE-2018-17461 in Chrome
Summary
by MITRE
An out of bounds read in PDFium in Google Chrome prior to 68.0.3440.75 allowed a remote attacker to perform an out of bounds memory read via a crafted PDF file.
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Analysis
by VulDB Data Team • 04/27/2020
The vulnerability identified as CVE-2018-17461 represents a critical out of bounds memory read flaw within PDFium, the embedded PDF rendering library used by Google Chrome and other applications. This issue emerged in versions of Chrome prior to 68.0.3440.75, where the PDFium component failed to properly validate memory access boundaries when processing maliciously crafted PDF files. The flaw resides in the library's handling of specific PDF structures that trigger improper memory traversal, allowing attackers to read data from memory locations outside the intended buffer boundaries. Such out of bounds reads typically occur when the application attempts to access memory locations beyond the allocated buffer limits, potentially exposing sensitive information stored in adjacent memory regions.
The technical implementation of this vulnerability involves the PDFium parser encountering malformed PDF objects or streams that cause it to compute incorrect memory offsets during document processing. When Chrome renders a crafted PDF file, the parser executes code paths that do not properly validate the size or structure of PDF elements, leading to memory access violations that can be exploited remotely. The out of bounds read behavior enables attackers to potentially extract arbitrary memory contents including sensitive data such as encryption keys, session tokens, or other confidential information stored in adjacent memory locations. This type of vulnerability falls under the Common Weakness Enumeration category CWE-125, which specifically addresses out-of-bounds read conditions in software implementations.
From an operational perspective, this vulnerability poses significant risks to Chrome users as it requires no user interaction beyond opening a malicious PDF file, making it particularly dangerous in phishing campaigns or exploit delivery scenarios. Attackers can craft PDF documents that trigger the out of bounds read when opened in Chrome, potentially leading to information disclosure attacks that could compromise user sessions or system security. The remote exploitation capability means that adversaries can deliver malicious payloads through web-based attack vectors without requiring local system access or user interaction beyond visiting a compromised website hosting the malicious PDF. This vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as the malicious PDF could contain embedded scripts that leverage the memory read flaw to extract sensitive data.
The mitigation strategy for CVE-2018-17461 primarily involves updating to Chrome version 68.0.3440.75 or later, where Google implemented proper bounds checking and memory validation in the PDFium library. Organizations should prioritize immediate patching of affected systems and consider implementing additional security controls such as PDF sandboxing, content filtering, and network-based intrusion detection systems to monitor for exploitation attempts. Security teams should also conduct vulnerability assessments to identify systems running older versions of Chrome or applications that may be affected by similar issues in the PDFium library. The fix typically involves adding proper input validation, bounds checking, and memory access controls to prevent the parser from traversing invalid memory locations while maintaining proper PDF rendering functionality.