CVE-2026-10634 Use-after-free in Zephyr native TCP `net_tcp_foreach()` due to dropping `tcp_lock` during the callback
A use-after-free in Zephyr's TCP stack allows attackers to cause system crashes or potentially disclose information via concurrent connection handling.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-10634?
CVE-2026-10634 is a medium-severity use after free vulnerability in Zephyrproject Zephyr, published on 15 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
Zephyr's native TCP stack iterates the global connection list in net_tcp_foreach() (subsys/net/ip/tcp.c) using the SYS_SLIST_FOR_EACH_CONTAINER_SAFE macro, which caches a pointer to the next list node. Prior to this fix the function released tcp_lock while invoking the per-connection callback and re-acquired it afterwards.
During that window a concurrent tcp_conn_release(), running on the dedicated TCP work-queue thread when a connection's reference count drops to zero (e.g. a remote peer closing or resetting the connection), can remove and k_mem_slab_free() the cached next connection. When the iterator advances it dereferences the freed (and possibly reallocated) slab memory — a use-after-free that can crash the system (denial of service) and, if the slot has been reused, cause the callback to operate on an attacker-influenced object (potential information disclosure or further fault).
net_tcp_foreach() is reached in production via the net conn network shell command and via net_tcp_close_all_for_iface() on interface-down; the freeing side is driven by ordinary TCP traffic.
The fix moves the connection/context teardown in tcp_conn_release() inside the tcp_lock critical section and keeps tcp_lock held across the callback in net_tcp_foreach(). The defect was introduced with the modern (TCP2) stack in 2020 and affects releases up to and including v4.4.0.
Weakness: CWE-416
Which versions are affected by CVE-2026-10634?
It affects 1 product.
Products include Zephyrproject Zephyr.
How do I fix CVE-2026-10634?
No fix has been published for CVE-2026-10634 yet. Limit exposure of the affected software until one is available.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-10634 being exploited?
There is no known exploitation of CVE-2026-10634 in the wild and no public exploit code.
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Sources
Also known as GHSA-6c57-xfhw-j26x.