CVE-2026-35217 NanoMQ Incorrectly Accepts a Malformed SUBSCRIBE and Can Be Driven into an ASAN-Detectable Out-of-Bounds Read
Attackers can trigger an out-of-bounds read and accept malformed subscriptions in NanoMQ, potentially causing crashes or leaking 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-2026-35217?
CVE-2026-35217 is a medium-severity memory corruption vulnerability in nanomq, published on 20 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
NanoMQ contains a protocol-semantics flaw in its MQTT v5 `SUBSCRIBE` handling: if a subscription entry is missing the final 1-byte `Subscription Options` field, the broker may still accept the malformed packet and install the subscription into internal broker state. Under a specific packet-length construction, the same parser flaw also causes a 1-byte out-of-bounds read that crosses the real heap allocation boundary and is detected by ASAN as a `heap-buffer-overflow`.
If the consumed byte happens to look acceptable, NanoMQ may continue and append the malformed subscription entry into its internal `subinfol` state. In that case, a `SUBSCRIBE` packet that should be rejected by MQTT rules is instead treated as a successful subscription. Whether ASAN reports the bug does not depend on MQTT's logical `remain` boundary; it depends on whether the read crosses the real heap allocation boundary of the underlying message buffer. In other words, these are not two unrelated issues. They are two manifestations of the same parsing defect: by default, it appears as a semantic vulnerability, and under suitable input conditions, it also becomes a verifiable out-of-bounds read vulnerability.
Weakness: CWE-125
Which versions are affected by CVE-2026-35217?
How do I fix CVE-2026-35217?
No fix has been published for CVE-2026-35217 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-2026-35217 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-35217 exists.
Sources
Also known as GHSA-w4xh-p384-w556.