CVE-2026-78955 in Chrome
Summary
by MITRE • 08/26/2026
Observable discrepancy in PerformanceAPIs in Google Chrome prior to 152.0.7977.65 allowed a remote attacker to potentially obtain cross-origin data via a crafted HTML page. (Chromium security severity: Medium)
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Analysis
by VulDB Data Team • 08/26/2026
The vulnerability identified within the performance monitoring subsystem of Google Chrome, specifically affecting versions prior to 152.0.7977.65, represents a significant breach in browser isolation mechanisms. This flaw resides in the implementation of Performance APIs, which are designed to provide web developers with detailed metrics regarding page load times, resource loading sequences, and script execution durations. While these tools are essential for optimizing user experience, they inadvertently expose timing information that can be leveraged by malicious actors to infer sensitive data across different origins. The core issue stems from an observable discrepancy in how performance timestamps are calculated or exposed when a crafted HTML page interacts with resources hosted on a different domain than the one currently active in the browser tab. This inconsistency allows for side-channel attacks where timing differences serve as a proxy for accessing restricted information, effectively bypassing standard cross-origin restrictions that should otherwise prevent such data leakage.
From a technical perspective, this vulnerability exploits the precision of high-resolution timers available through the Performance API. When an attacker controls or influences the loading environment of a victim's browser session, they can measure the time it takes for specific network requests to complete or for scripts to execute. By carefully crafting HTML pages that trigger these performance measurements under controlled conditions, an adversary can detect minute variations in response times. These variations often correlate with whether certain resources were successfully loaded from cache versus being fetched anew from a remote server, or even whether specific content exists on the target origin. This technique transforms what should be benign diagnostic data into a powerful vector for cross-origin information disclosure, allowing the attacker to reconstruct parts of the victim's browsing history or access private application states without direct permission.
The operational impact of this vulnerability is primarily centered around privacy violations and potential reconnaissance activities against web applications that rely on strict isolation policies. An attacker utilizing this flaw could potentially determine if a user has previously visited specific sites, accessed particular resources, or even infer the presence of sensitive files based on timing anomalies. This capability undermines the fundamental security model of modern browsers, which relies heavily on the Same-Origin Policy to protect user data. Although classified as medium severity by Chromium’s internal metrics due to the complexity required for exploitation and the indirect nature of the data access, the implications are severe in targeted attacks where such information can be combined with other vectors to compromise account security or conduct sophisticated social engineering campaigns based on accurate knowledge of a victim's digital footprint.
Mitigation strategies must focus on both immediate patching and long-term architectural improvements within browser performance monitoring tools. The primary defense is upgrading Google Chrome to version 152.0.7977.65 or later, where the underlying logic governing these APIs has been corrected to eliminate the observable discrepancies that facilitate timing-based attacks. For organizations unable to immediately patch all endpoints, implementing strict Content Security Policy directives can help mitigate some risks by restricting which origins are allowed to execute scripts and access performance data. Additionally, developers should avoid relying on high-resolution timers for security-sensitive decisions or sensitive state checks within client-side applications. Industry standards such as CWE-208, which covers observable timing discrepancies, highlight the importance of ensuring that system responses do not leak information through temporal variations. Furthermore, this vulnerability aligns with ATT&CK technique T1537, involving data exfiltration over alternative channels, emphasizing the need for continuous monitoring and updated browser configurations to prevent such side-channel leaks from compromising user privacy and organizational security postures.