CVE-2026-21888: MQTT v5 Variable Byte Integer parsing out-of-bounds: get_var_integer()

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-03-11 · updated 2026-06-17
Weakness: CWE-125

Description

NanoMQ MQTT Broker (NanoMQ) is an all-around Edge Messaging Platform. MQTT v5 Variable Byte Integer parsing out-of-bounds: get_var_integer() accepts 5-byte varints without bounds checks; reliably triggers OOB read / crash when built with ASan. This affects 0.24.6 and earlier.

Affected products

nanomq: through 0.24.6

References

https://github.com/nanomq/nanomq/issues/2192
https://github.com/nanomq/nanomq/security/advisories/GHSA-cggc-6m7w-j7x5

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