CVE-2025-56352
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk20th percentile - higher than 20% of all known CVEs
Summary
In tinyMQTT, due to a bug in handling CONNECT packets, the broker fails to close the TCP connection after receiving a packet with a zero-length Client ID when CleanSession is set to 0. This leads to server resource exhaustion with repeated connection attempts.
Risk Assessment
The organization may experience denial of service due to server resource exhaustion, which can impact the availability of services relying on the MQTT broker.
Recommendation
It is recommended to update to the latest version of tinyMQTT to fix this issue and to monitor TCP connections to detect and mitigate invalid connection attempts.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

