How severe is CVE-2021-3967?

CVE-2021-3967 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-3967 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (53rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-3967?

CVE-2021-3967 affects Zulip. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-3967?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-3967 published?

CVE-2021-3967 was published on 2022-02-26 and last updated on 2026-06-17.

CVE-2021-3967

CVE-2021-3967 is a high-severity vulnerability in Zulip with a CVSS 3.x base score of 8.8. 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-284.

Key facts

Severity: High (CVSS 3.x base score 8.8)
CVSS v2: 6.5
EPSS exploit prediction: 1% (53rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-284
Affected product: Zulip
Published: 2022-02-26
Last modified: 2026-06-17

Description

Improper Access Control in GitHub repository zulip/zulip prior to 4.10.

Frequently asked questions

What is CVE-2021-3967?: Improper Access Control in GitHub repository zulip/zulip prior to 4.10.
How severe is CVE-2021-3967?: CVE-2021-3967 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-3967 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (53rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-3967?: CVE-2021-3967 affects Zulip. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-3967?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-3967 published?: CVE-2021-3967 was published on 2022-02-26 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:zulip:zulip:*:*:*:*:*:*:*:*

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