CVE-2025-9866: Google Chrome · Inappropriate Implementation
Affects Google ChromeSource CVE Database V5
Not known to be exploited · CVSS 8.8 High.
Data as of 26 Oct 2026, 10:12 UTC
- EPSS
- 0.5% chance of exploitation in 30 days – higher than 42% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 3 Sep 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| Google Chrome | Affected
| Fixed in– |
AI-suggested
To mitigate the risks posed by CVE-2025-9866, organizations should immediately update all Google Chrome installations to version 140.0.7339.80 or later once the patch is available. Until patches are applied, organizations should consider restricting or disabling Chrome extensions, especially those not vetted or from untrusted sources, to reduce the attack surface. Implementing strict extension management policies via enterprise tools can help enforce this. Network-level protections such as web filtering and blocking access to known malicious domains can reduce the likelihood of users encountering crafted HTML pages designed to exploit this vulnerability. User awareness training focused on phishing and social engineering can further reduce risk by discouraging clicking on suspicious links. Security teams should monitor browser telemetry and logs for unusual extension behavior or CSP violations. Employing Content Security Policy reporting features can help detect attempted bypasses. Finally, organizations should maintain up-to-date endpoint detection and response (EDR) solutions capable of identifying anomalous script execution within browsers.
Description
Inappropriate implementation in Extensions in Google Chrome prior to 140.0.7339.80 allowed a remote attacker to bypass content security policy via a crafted HTML page. (Chromium security severity: Medium)