Eclipse Paho Go MQTT may incorrectly encode strings if length exceeds 65535 bytes

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.3 · 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 · score source

EPSS

• CVE-2025-10543: 0.24% estimated exploitation activity in the next 30 days; percentile 15.57 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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).

Published by the source

2 Dec 2025, 09:30 UTC

Last modified by the source

17 Dec 2025, 00:43 UTC

Source last checked

26 Oct 2026, 15:13 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-32fw-gq77-f2f2

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# Patch Next advisory brief: CVE-2025-10543

Advisory: Eclipse Paho Go MQTT may incorrectly encode strings if length exceeds 65535 bytes
IDs: CVE-2025-10543, GHSA-32fw-gq77-f2f2
Record: https://patchnext.com/advisories/cve-2025-10543 (revision 1, source checked 26 Oct 2026, 15:13 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/eclipse/paho.mqtt.golang 1.5.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/eclipse/paho.mqtt.golang: affected < 1.5.1; fixed in 1.5.1

## Suggested inspection (read-only)
- Go github.com/eclipse/paho.mqtt.golang: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/eclipse/paho.mqtt.golang.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-32fw-gq77-f2f2 (GitHub-reviewed advisory GHSA-32fw-gq77-f2f2 lists affected ranges: Go github.com/eclipse/paho.mqtt.golang >=0 <1.5.1)

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