CVE-2021-34434Network attack vector

Unauthorized message access via stale durable subscriptions

Published Aug 30, 2021 · Updated Aug 4, 2024

Incorrect authorization in Eclipse Mosquitto 2.0.0 through 2.0.11 allows remote authenticated users to retain revoked topic access. The dynamic security plugin updates a client ACL but fails to remove subscriptions stored for that client while its durable session is offline. The client must already have an authenticated durable session and a subscription; after access is revoked, reconnecting continues delivery from the previously authorized topic.

CVSS severity5.3
Medium
EPSS probability1.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect authorization in Eclipse Mosquitto 2.0.0 through 2.0.11 allows remote authenticated users to retain revoked topic access. The dynamic security plugin updates a client ACL but fails to remove subscriptions stored for that client while its durable session is offline. The client must already have an authenticated durable session and a subscription; after access is revoked, reconnecting continues delivery from the previously authorized topic.

The record

CVE
CVE-2021-34434
Published
Aug 30, 2021
Updated
Aug 4, 2024
Vendor
The Eclipse Foundation
Product
Eclipse Mosquitto
Classifications
CWE-285, CWE-863
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 30, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.0 <unspecified
  2. Affected versionversion=unspecified <=2.0.11

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

The Eclipse Foundation · Eclipse Mosquittoversion=2.0 <unspecified; version=unspecified <=2.0.11

Published CVSS scores

5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-285Improper Authorization
CWE-863Incorrect Authorization

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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