CVE-2021-21209Network attack vector

Cross-origin data leakage via storage-size side channel

Published Apr 26, 2021 · Updated Aug 3, 2024

Cross-origin data exposure in Google Chrome before 90.0.4430.72 allows remote attackers to infer response sizes via crafted HTML. The storage implementation lets an attacker page bypass response-padding countermeasures and use storage changes to measure a cross-origin response. A victim must visit the crafted page while authenticated state makes a target response differ; the leak reveals response-derived facts rather than response bodies.

CVSS severity6.5
Medium
EPSS probability1.01%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-origin data exposure in Google Chrome before 90.0.4430.72 allows remote attackers to infer response sizes via crafted HTML. The storage implementation lets an attacker page bypass response-padding countermeasures and use storage changes to measure a cross-origin response. A victim must visit the crafted page while authenticated state makes a target response differ; the leak reveals response-derived facts rather than response bodies.

The record

CVE
CVE-2021-21209
Published
Apr 26, 2021
Updated
Aug 3, 2024
Vendor
Google Cloud
Product
Google Chrome
Classifications
CWE-200
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 26, 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 <90.0.4430.72

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Google Cloud · Google Chromeversion=unspecified <90.0.4430.72

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:P/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-200Exposure of Sensitive Information to an Unauthorized Actor

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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