How severe is CVE-2021-21126?

CVE-2021-21126 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2021-21126 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 9% (95th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-21126?

CVE-2021-21126 primarily affects Google Chrome. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-21126?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-21126 published?

CVE-2021-21126 was published on 2021-02-09 and last updated on 2026-06-17.

CVE-2021-21126

CVE-2021-21126 is a medium-severity vulnerability in Google Chrome with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
CVSS v2: 4.3
EPSS exploit prediction: 9% (95th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Google Chrome
Published: 2021-02-09
Last modified: 2026-06-17

Description

Insufficient policy enforcement in extensions in Google Chrome prior to 88.0.4324.96 allowed a remote attacker to bypass site isolation via a crafted Chrome Extension.

Frequently asked questions

What is CVE-2021-21126?: Insufficient policy enforcement in extensions in Google Chrome prior to 88.0.4324.96 allowed a remote attacker to bypass site isolation via a crafted Chrome Extension.
How severe is CVE-2021-21126?: CVE-2021-21126 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2021-21126 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 9% (95th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-21126?: CVE-2021-21126 primarily affects Google Chrome. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-21126?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-21126 published?: CVE-2021-21126 was published on 2021-02-09 and last updated on 2026-06-17.

References

Affected products (2)

cpe:2.3:a:google:chrome:*:*:*:*:*:*:*:*
cpe:2.3:a:microsoft:edge_chromium:*:*:*:*:*:*:*:*

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