CVE-2026-121237 in Chrome
Summary
by MITRE • 11/03/2026
Improper state validation in FileSystem in Google Chrome prior to 157.0.8103.38 allowed a remote attacker leveraging social engineering to bypass system access restrictions via a crafted HTML page. (Chromium security severity: Medium)
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified as an improper state validation within the FileSystem API of Google Chrome prior to version 157.0.8103.38 represents a significant deviation from expected browser security boundaries. This flaw resides in how the Chromium engine manages and validates the internal states associated with file system operations, specifically when interacting with user-accessible directories or sandboxed storage areas. The core technical deficiency lies in the failure to rigorously verify that the current state of the FileSystem object aligns with the permissions granted by the browser's security model before allowing subsequent read or write actions. This lack of strict validation creates a window where an attacker can manipulate the context of file operations, effectively tricking the browser into executing commands outside its intended scope. The severity is classified as Medium within the Chromium security framework, indicating that while exploitation requires specific conditions, it poses a tangible risk to user data integrity and system access controls.
Exploitation of this vulnerability relies heavily on social engineering tactics rather than automated remote code execution vectors. A malicious actor would need to host or distribute a crafted HTML page designed to trigger the flawed state validation logic within the FileSystem API. When an unsuspecting user visits this webpage, typically through phishing emails, compromised websites, or deceptive advertisements, their browser processes the script without raising immediate security alerts due to the nuanced nature of the state mismatch. The attacker leverages this discrepancy to bypass system access restrictions that are normally enforced by Chrome's same-origin policy and sandboxing mechanisms. By manipulating the perceived state of a file handle or directory entry, the malicious code can gain unauthorized read or write access to files that should remain protected from web-based scripts. This allows for potential data exfiltration or the placement of persistent malware payloads in locations where standard web applications do not have permission to operate.
The operational impact of this vulnerability extends beyond simple data theft, as it undermines the fundamental trust model of the browser environment. Users who rely on Chrome for secure browsing and sensitive tasks may find their local file systems compromised without explicit consent or clear warning indicators. The ability to bypass access restrictions means that attackers can potentially access personal documents, configuration files, or application-specific data stored in user directories. This breach of isolation weakens the defense-in-depth strategy employed by modern web browsers, where each tab and extension is expected to operate within a confined sandbox. If an attacker successfully exploits this state validation flaw, they may establish a foothold on the victim's machine that can be leveraged for further attacks, such as credential harvesting or lateral movement in enterprise environments if Chrome is used with elevated privileges or integrated into broader identity management systems.
Mitigation strategies primarily focus on timely software updates and enhanced user awareness. The most effective remediation is to upgrade Google Chrome to version 157.0.8103.38 or later, where the state validation logic has been corrected to ensure that all file system operations are strictly bound by their declared permissions and current context. Organizations should enforce automated update policies to minimize the window of exposure for end-users. Additionally, since exploitation requires social engineering, security awareness training is critical in helping users identify suspicious links and untrusted web content. Implementing browser hardening techniques, such as restricting file system API access via enterprise policies or using extensions that monitor DOM manipulation, can provide an additional layer of defense against similar state-based attacks.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation, specifically in the context of application logic and state management rather than raw data parsing. The failure to validate the internal state before permitting file system access allows for unauthorized actions that violate intended security policies. In terms of offensive cybersecurity frameworks, this exploit maps to MITRE ATT&CK techniques related to Collection via File and Directory Discovery or Data from Information Repositories, depending on whether the attacker is reading existing data or writing new files. Understanding these mappings helps security teams prioritize detection rules and incident response procedures for similar state manipulation vulnerabilities in web browsers and other client-side applications that interact with local resources.