How severe is CVE-2021-34434?

CVE-2021-34434 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-2021-34434 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (69th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-34434?

CVE-2021-34434 primarily affects Eclipse Mosquitto. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-34434?

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

When was CVE-2021-34434 published?

CVE-2021-34434 was published on 2021-08-30 and last updated on 2026-06-17.

CVE-2021-34434

CVE-2021-34434 is a medium-severity vulnerability in Eclipse Mosquitto 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-863.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
CVSS v2: 5.0
EPSS exploit prediction: 1% (69th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-863
Affected product: Eclipse Mosquitto
Published: 2021-08-30
Last modified: 2026-06-17

Description

In Eclipse Mosquitto versions 2.0 to 2.0.11, when using the dynamic security plugin, if the ability for a client to make subscriptions on a topic is revoked when a durable client is offline, then existing subscriptions for that client are not revoked.

Frequently asked questions

What is CVE-2021-34434?: In Eclipse Mosquitto versions 2.0 to 2.0.11, when using the dynamic security plugin, if the ability for a client to make subscriptions on a topic is revoked when a durable client is offline, then existing subscriptions for that client are not revoked.
How severe is CVE-2021-34434?: CVE-2021-34434 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-2021-34434 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (69th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-34434?: CVE-2021-34434 primarily affects Eclipse Mosquitto. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-34434?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-34434 published?: CVE-2021-34434 was published on 2021-08-30 and last updated on 2026-06-17.

References

Affected products (3)

cpe:2.3:a:eclipse:mosquitto:*:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*

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