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Vulnerability record · CVE-2025-56352 · published 18 May 2026

CVE-2025-56352: Uncontrolled resource consumption vulnerability

In tinyMQTT commit 6226ade15bd4f97be2d196352e64dd10937c1962 (2024-02-18), the broker mishandles protocol violations during CONNECT packet parsing. When receiving a CONNECT packet with a zero-length Client ID while CleanSession is set to 0, the broker correctly replies with a CONNACK return code 0x02 (Identifier Rejected) but fails to explicitly close the TCP connection. Since the surrounding connection teardown logic is not guaranteed to execute, each such invalid CONNECT attempt leaves the underlying socket open. Repeated attempts cause server-side resource exhaustion due to accumulating file descriptors and memory usage, potentially resulting in denial of service.

7.5 CVSS 3.1 High EPSS 0.28% · top 81.8% CWE-400 · Uncontrolled resource consumption Deferred
7.5CVSS 3.1 base score
0.28%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
2References
17 Jun 2026Last modified by NVD

Description

In tinyMQTT commit 6226ade15bd4f97be2d196352e64dd10937c1962 (2024-02-18), the broker mishandles protocol violations during CONNECT packet parsing. When receiving a CONNECT packet with a zero-length Client ID while CleanSession is set to 0, the broker correctly replies with a CONNACK return code 0x02 (Identifier Rejected) but fails to explicitly close the TCP connection. Since the surrounding connection teardown logic is not guaranteed to execute, each such invalid CONNECT attempt leaves the underlying socket open. Repeated attempts cause server-side resource exhaustion due to accumulating file descriptors and memory usage, potentially resulting in denial of service.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

LinkTags
https://github.com/JustDoIt0910/tinyMQTT/issues/19
https://github.com/user-attachments/files/21207896/Resource_Exhaustion_Poc.txt

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Source: NIST National Vulnerability Database (record CVE-2025-56352), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.