---
id: "CVE-2021-30533"
kind: "vulnerability"
aliases: ["CVE-2021-30533"]
title: "Insufficient policy enforcement in PopupBlocker in Google Chrome prior to 91.0.4472.77 allowed a remote attacker to\u2026"
severity: "medium"
cvss: 6.5
epss: 0.16742
exploited: true
status: "open"
category: "runtime"
products: [{"name": "Google Chromium PopupBlocker", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "google chrome", "fixed": ["91.0.4472.77"], "affected": "< 91.0.4472.77", "ecosystem": "vendor"}, {"name": "fedoraproject fedora", "fixed": [], "affected": "= 33", "ecosystem": "vendor"}, {"name": "fedoraproject fedora", "fixed": [], "affected": "= 34", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["browser-users", "chrome", "chromium", "edge", "exploited", "opera", "runtime"]
not_affected_if: ["fully-patched-browser"]
published_at: "2021-06-07T20:15:08+00:00"
first_seen_at: "2026-10-23T19:11:52+00:00"
updated_at: "2026-10-23T22:29:04+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-30533", "first_seen_at": "2026-10-23T19:11:52+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2021-30533", "first_seen_at": "2026-10-23T19:13:45+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-30533", "first_seen_at": "2026-10-23T22:29:04+00:00"}]
---

# Insufficient policy enforcement in PopupBlocker in Google Chrome prior to 91.0.4472.77 allowed a remote attacker to…

Chromium's popup blocker has an insufficient policy enforcement flaw that lets a remote web page bypass navigation restrictions using a crafted iframe. An attacker gets a page that can navigate or open content it should be blocked from, and the flaw is listed as actively exploited.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Google Chromium PopupBlocker affected ? fixed ?
- vendor:google chrome affected < 91.0.4472.77 fixed 91.0.4472.77
- vendor:fedoraproject fedora affected = 33 fixed ?
- vendor:fedoraproject fedora affected = 34 fixed ?

## How to check

Check the installed browser version against the vendor's patched release (sources do not give the fixed version).

## Fix

Update Chrome, Edge, Opera and other Chromium-based browsers to the latest vendor release, as CISA directs.

## Timeline

- 2026-10-23T19:11:52+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-30533
- 2026-10-23T19:13:45+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2021-30533
- 2026-10-23T22:29:04+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-30533

## From the sources

Google Chromium PopupBlocker contains an insufficient policy enforcement vulnerability that allows a remote attacker to bypass navigation restrictions via a crafted iframe. This vulnerability could affect multiple web browsers that utilize Chromium, including, but not limited to, Google Chrome, Microsoft Edge, and Opera.

CISA required action: Apply updates per vendor instructions.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_