CVE-2026-121125 in Chrome
Summary
by MITRE • 11/03/2026
Information leak in ServiceWorker in Google Chrome prior to 157.0.8103.38 allowed a remote attacker who had compromised the renderer process to obtain sensitive information via a crafted HTML page. (Chromium security severity: Low)
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified as an information leak within the ServiceWorker component of Google Chrome prior to version 157.0.8103.38 represents a significant breach in process isolation boundaries, specifically affecting the mechanism by which web applications manage background tasks and offline capabilities. This flaw allows for the unauthorized exfiltration of sensitive data that should remain confined within specific execution contexts. The root cause lies in how ServiceWorker instances handle state management and resource caching when interacting with compromised renderer processes. In a typical browser architecture, each tab or frame operates within its own sandboxed renderer process to prevent cross-site scripting attacks from escalating into full system compromise. However, this vulnerability exploits the communication channels between these isolated renderers and the more privileged service worker threads, enabling an attacker who has already achieved code execution within a renderer process to bypass expected security controls and access data intended for other contexts or internal browser operations.
From a technical perspective, the flaw stems from improper validation of cross-process messages or shared memory regions utilized by ServiceWorker APIs. When a malicious HTML page is crafted to exploit this weakness, it can leverage specific API calls that trigger unintended side effects in the service worker thread. This allows the attacker to read sensitive information such as cookies, local storage data, or cached resources belonging to other sites or even internal browser states. The severity of this issue is classified as Low by Chromium security standards because it requires a pre-existing compromise of the renderer process. Nevertheless, the ability to escalate from renderer-level code execution to accessing broader application state significantly increases the blast radius of an initial web-based attack vector. This aligns with CWE-200, which categorizes such issues under Information Exposure, where sensitive information is disclosed without proper authorization or access controls.
The operational impact of this vulnerability extends beyond simple data theft; it undermines the fundamental trust model of modern web browsers. If an attacker can reliably extract sensitive information from a compromised renderer via ServiceWorker interactions, they can potentially build more sophisticated attack chains that combine client-side exploits with server-side attacks through session hijacking or credential harvesting. This is particularly dangerous in environments where users frequently interact with multiple tabs and applications simultaneously, as the isolation between these contexts becomes porous. The vulnerability also impacts user privacy by allowing malicious scripts to fingerprint browser state or steal authentication tokens stored within service worker caches. Such capabilities can facilitate long-term persistence for attackers who maintain access to a victim's machine through persistent web-based footholds.
Mitigation strategies primarily involve updating Google Chrome to version 157.0.8103.38 or later, where the underlying logic governing ServiceWorker message passing and state isolation has been hardened. For organizations unable to patch immediately due to compatibility concerns, implementing strict Content Security Policy directives can help mitigate some risks by restricting script execution sources and preventing unauthorized data exfiltration channels. Additionally, enabling site-isolation features ensures that each origin runs in its own renderer process with dedicated background partitions for service workers, thereby reducing the attack surface available to an attacker who has compromised a single tab. Monitoring browser logs for unusual ServiceWorker registration patterns or excessive cache access requests can also aid in detecting potential exploitation attempts. This vulnerability is mapped to MITRE ATT&CK technique T1059, specifically within the context of command and control via web protocols, as it enables attackers to use legitimate browser features to exfiltrate data undetected by traditional network security tools.