How severe is CVE-2021-34431?

CVE-2021-34431 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-34431 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (65th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-34431?

CVE-2021-34431 affects Eclipse Mosquitto. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-34431?

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

When was CVE-2021-34431 published?

CVE-2021-34431 was published on 2021-07-22 and last updated on 2026-06-17.

CVE-2021-34431

CVE-2021-34431 is a medium-severity vulnerability in Eclipse Mosquitto 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-401.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
CVSS v2: 4.0
EPSS exploit prediction: 1% (65th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-401
Affected product: Eclipse Mosquitto
Published: 2021-07-22
Last modified: 2026-06-17

Description

In Eclipse Mosquitto version 1.6 to 2.0.10, if an authenticated client that had connected with MQTT v5 sent a crafted CONNECT message to the broker a memory leak would occur, which could be used to provide a DoS attack against the broker.

Frequently asked questions

What is CVE-2021-34431?: In Eclipse Mosquitto version 1.6 to 2.0.10, if an authenticated client that had connected with MQTT v5 sent a crafted CONNECT message to the broker a memory leak would occur, which could be used to provide a DoS attack against the broker.
How severe is CVE-2021-34431?: CVE-2021-34431 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-34431 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (65th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-34431?: CVE-2021-34431 affects Eclipse Mosquitto. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-34431?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-34431 published?: CVE-2021-34431 was published on 2021-07-22 and last updated on 2026-06-17.

References

https://bugs.eclipse.org/bugs/show_bug.cgi?id=573191

Affected products (1)

cpe:2.3:a:eclipse:mosquitto:*:*:*:*:*:*:*:*

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CVE-2018-12550 — High (CVSS 8.1): When Eclipse Mosquitto version 1.0 to 1.5.5 (inclusive) is configured to use an ACL file, and that ACL file is empty,…
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CVE-2023-5632 — High (CVSS 7.5): In Eclipse Mosquito before and including 2.0.5, establishing a connection to the mosquitto server without sending data…
CVE-2023-28366 — High (CVSS 7.5): The broker in Eclipse Mosquitto 1.3.2 through 2.x before 2.0.16 has a memory leak that can be abused remotely when a…

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Other CWE-401 (Missing Release of Memory after Effective Lifetime) vulnerabilities

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CVE-2025-21954 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: netmem: prevent TX of unreadable skbs Currently…
CVE-2024-57947 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_set_pipapo: fix initial map…
CVE-2024-56779 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: nfsd: fix nfs4_openowner leak when concurrent…
CVE-2024-36911 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: hv_netvsc: Don't free decrypted memory In CoCo…

Browse all CWE-401 (Missing Release of Memory after Effective Lifetime) vulnerabilities →

Threat intelligence

Threat-intel indicators referencing this CVE:

182.95.217.202 (ipv4-addr)
182.95.106.102 (ipv4-addr)
128.185.208.42 (ipv4-addr)
122.186.202.58 (ipv4-addr)
182.95.190.150 (ipv4-addr)
152.52.192.162 (ipv4-addr)
182.95.185.158 (ipv4-addr)
182.95.101.182 (ipv4-addr)