How severe is CVE-2021-30479?

CVE-2021-30479 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2021-30479 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-30479?

CVE-2021-30479 affects Zulip Zulip Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-30479?

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

When was CVE-2021-30479 published?

CVE-2021-30479 was published on 2021-04-15 and last updated on 2026-06-17.

CVE-2021-30479

CVE-2021-30479 is a medium-severity vulnerability in Zulip Zulip Server with a CVSS 3.x base score of 5.3. 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-269.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
CVSS v2: 5.0
EPSS exploit prediction: 1% (54th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-269
Affected product: Zulip Zulip Server
Published: 2021-04-15
Last modified: 2026-06-17

Description

An issue was discovered in Zulip Server before 3.4. A bug in the implementation of the all_public_streams API feature resulted in guest users being able to receive message traffic to public streams that should have been only accessible to members of the organization.

Frequently asked questions

What is CVE-2021-30479?: An issue was discovered in Zulip Server before 3.4. A bug in the implementation of the all_public_streams API feature resulted in guest users being able to receive message traffic to public streams that should have been only accessible to members of the organization.
How severe is CVE-2021-30479?: CVE-2021-30479 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2021-30479 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-30479?: CVE-2021-30479 affects Zulip Zulip Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-30479?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-30479 published?: CVE-2021-30479 was published on 2021-04-15 and last updated on 2026-06-17.

References

https://blog.zulip.com/2021/04/14/zulip-server-3-4/

Affected products (1)

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

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