CVE-2021-21163Network attack vector

Cross-origin data leak via Reader Mode validation

Published Mar 9, 2021 · Updated Aug 3, 2024

Insufficient data validation in Google Chrome Reader Mode on iOS before 89.0.4389.72 allows remote attackers to leak cross-origin data. Public advisories identify Reader Mode but do not disclose the specific input-validation operation that accepts the crafted HTML page. Exploitation requires a user to load attacker-controlled HTML that communicates with a malicious server; the reported consequence is data disclosure only.

CVSS severity6.5
Medium
EPSS probability0.94%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Insufficient data validation in Google Chrome Reader Mode on iOS before 89.0.4389.72 allows remote attackers to leak cross-origin data. Public advisories identify Reader Mode but do not disclose the specific input-validation operation that accepts the crafted HTML page. Exploitation requires a user to load attacker-controlled HTML that communicates with a malicious server; the reported consequence is data disclosure only.

The record

CVE
CVE-2021-21163
Published
Mar 9, 2021
Updated
Aug 3, 2024
Vendor
Google Cloud
Product
Google Chrome
Classifications
CWE-346, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 9, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <89.0.4389.72

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Google Cloud · Google Chromeversion=unspecified <89.0.4389.72

Published CVSS scores

4.3NIST National Vulnerability DatabaseAV:N/AC:M/Au:N/C:P/I:N/A:N
6.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-346Origin Validation Error
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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