CVE-2025-56352 Denial of service in n/a
An attacker can cause denial of service in the tinyMQTT broker by sending repeated invalid CONNECT packets that leak file descriptors and memory.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2025-56352?
CVE-2025-56352 is a high-severity denial of service vulnerability in n/a, published on 18 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-400
Which versions are affected by CVE-2025-56352?
How do I fix CVE-2025-56352?
No fix has been published for CVE-2025-56352 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-56352 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-56352 exists.
Sources
Also known as GHSA-m5jh-ppcv-76xr.