Vulnerability · Published Dec 2, 2025 · Assigned by eclipse
CVE-2025-10543
Medium 6.3
In plain English
A medium-severity security flaw in paho.mqtt.golang (Go MQTT v3.1 library) from Eclipse Foundation. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 16% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
In Eclipse Paho Go MQTT v3.1 library (paho.mqtt.golang) versions <=1.5.0 UTF-8 encoded strings, passed into the library, may be incorrectly encoded if their length exceeds 65535 bytes. This may lead to unexpected content in packets sent to the server (for example, part of an MQTT topic may leak into the message body in a PUBLISH packet). The issue arises because the length of the data passed in was converted from an int64/int32 (depending upon CPU) to an int16 without checks for overflows. The int16 length was then written, followed by the data (e.g. topic). This meant that when the data (e.g. topic) was over 65535 bytes then the amount of data written exceeds what the length field indicates. This could lead to a corrupt packet, or mean that the excess data leaks into another field (e.g. topic leaks into message body).
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/eclipse/paho.mqtt.golang | 1.5.1 | GHSA-32fw-gq77-f2f2 |
| Go | github.com/eclipse/paho.mqtt.golang | 1.5.1 | GO-2025-4173 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Eclipse Foundation | paho.mqtt.golang (Go MQTT v3.1 library) | 0 – through 1.5.0 |
Weakness: CWE-681, CWE-197 · Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N