CVE-2026-73863 NanoMQ: Heap-Buffer-Overflow in `nmq_subinfo_decode()` During MQTT v5 SUBSCRIBE Parsing
A remote attacker can crash the NanoMQ MQTT broker by sending a crafted SUBSCRIBE packet that triggers a heap buffer overflow during parsing.
- 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-2026-73863?
CVE-2026-73863 is a high-severity memory corruption vulnerability in nanomq, published on 18 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
NanoMQ is an MQTT broker. Prior to 0.24.14, NanoMQ's broker-side MQTT v5 nmq_subinfo_decode() function in nng/src/sp/protocol/mqtt/mqtt_parser.c reuses len_of_varint from the outer Properties Length while parsing each SUBSCRIPTION_IDENTIFIER. A remote client can send a SUBSCRIBE packet with a multi-byte Properties Length and repeated subscription identifiers, causing get_var_integer() to begin at an incorrect offset and read beyond the heap message buffer. The flaw is reachable through the broker receive path and can crash the broker, while the separately reported topic-option off-by-one occurs later and is not this vulnerability. This issue is fixed in version 0.24.14.
Weakness: CWE-125
Which versions are affected by CVE-2026-73863?
How do I fix CVE-2026-73863?
No fix has been published for CVE-2026-73863 yet. Limit exposure of the affected software until one is available.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-73863 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-73863 exists.
Sources
Also known as GHSA-pf97-vm7h-q84m.