CVE-2026-78959 in Chrome
Summary
by MITRE • 08/26/2026
Improper handling of case sensitivity in FileSystem in Google Chrome prior to 152.0.7977.65 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 • 08/26/2026
The vulnerability identified as an improper handling of case sensitivity within the FileSystem API in Google Chrome prior to version 152.0.7977.65 represents a significant deviation from expected secure coding practices regarding resource access control. This flaw stems from inconsistent normalization or comparison logic when resolving file paths and validating permissions against the underlying operating system's file system architecture. In many modern operating systems, such as Windows, file name comparisons are case-insensitive by default, whereas Unix-like systems treat them as case-sensitive. The browser engine failed to adequately reconcile these differences during the validation of access requests initiated through web pages. Consequently, an attacker could craft a malicious HTML page that exploits this discrepancy to trick the browser into granting access to files or directories that should remain restricted under normal security policies.
From a technical perspective, the core issue lies in how the FileSystem API processes path strings before checking them against the user's granted permissions. When a web application requests read or write access to specific locations within the local file system, it must undergo a permission check mediated by the browser's sandboxing mechanisms. The vulnerability allows an attacker to manipulate the case of characters in the requested file paths. For instance, if a restriction is applied to a directory named Documents, but the underlying OS treats documents and DOCUMENTS as identical or resolves them to the same inode without proper canonicalization during the permission check phase, the browser may incorrectly conclude that access has been granted when it has not. This bypasses the intended isolation boundaries designed to protect user data from unauthorized web-based access.
The operational impact of this vulnerability is primarily driven by social engineering tactics rather than automated exploitation vectors. A remote attacker cannot force a victim's browser to execute arbitrary code or access files without interaction. Instead, the attack requires convincing the user to visit a malicious website and explicitly grant file system permissions through standard browser prompts. Once these permissions are granted, often under false pretenses such as needing to upload a document for a legitimate-looking service, the attacker can leverage the case sensitivity flaw to read sensitive configuration files, personal documents, or other restricted resources that were not intended to be accessible by the web application. This leads to potential data exfiltration and privacy violations, undermining the trust model of the browser's security architecture.
This vulnerability aligns with CWE-20 Improper Input Validation, specifically regarding the failure to normalize input before performing access control decisions. It also relates to CWE-732 Incorrect Permission Assignment for Critical Resource, as the permission check logic was flawed due to case handling errors. In terms of offensive cyber operations and threat modeling, this behavior is consistent with techniques found in MITRE ATT&CK framework under T1059 Command and Scripting Interpreter or more specifically within data staging and collection phases where attackers use social engineering to gain initial access before escalating privileges via local file system interactions. The severity rating of Medium reflects the dependency on user interaction but acknowledges the potential for significant data loss if successful.
Mitigation strategies focus heavily on both software updates and defensive configuration practices. Users must ensure that Google Chrome is updated to version 152.0.7977.65 or later, where this case sensitivity logic has been corrected to enforce strict canonicalization of file paths before permission validation. For organizations deploying Chrome via enterprise policies, enforcing automatic update mechanisms can prevent exposure windows from opening. Additionally, security awareness training is critical in mitigating the social engineering aspect; users should be educated to scrutinize any request for local file system access, verifying the legitimacy and necessity of such permissions before granting them. Implementing strict Content Security Policies (CSP) where applicable can also limit the ability of malicious scripts to interact with sensitive APIs, although this specific vulnerability requires direct user consent via permission prompts which CSP cannot entirely prevent without breaking legitimate functionality.