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VulnerabilityPublished Updated

CVE-2026-10653: zephyrproject zephyr · Use After Free

Affects zephyrproject zephyrSource CVE Database V5

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Not known to be exploited · CVSS 6.4 Medium : upgrade to 4.4.2 or 4.3.1 when convenient.

Data as of 13 Nov 2026, 23:53 UTC

CVSS 3.1 base score
6.4Medium
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (zephyr)CVSS 3.16.4
EPSS
0.4% chance of exploitation in 30 days – higher than 36% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 4.4.2, 4.3.1
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 30 Jun 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.

What to do

Upgrade zephyrproject zephyr to 4.4.2 or 4.3.1.

Affected software

ProductAffectedFixed in
zephyrprojectzephyrAffected
  • >=4.4.0 <4.4.2
Fixed in
  • 4.4.2
zephyrprojectzephyrAffected
  • >=2.7.0 <4.3.1
Fixed in
  • 4.3.1
GitHubzephyrpkg:github/zephyrOther threatsAffected
  • >=2.7.0 <4.3.1
  • >=4.4.0 <4.4.2
Fixed in
  • 4.3.1
  • 4.4.2

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix converting reference counts to atomic operations is available on the main branch and backported to Zephyr v4.3 and v4.4 branches. The v3.7 LTS branch remains vulnerable as the fix was not backported due to incompatibilities. Users of v3.7 should serialize net_buf_unref() calls in their applications to avoid concurrent unref races. Check the official Zephyr project advisories and repositories for the latest patches and guidance.

Description

The Zephyr net_buf library (lib/net_buf/buf.c) manipulated both of its reference counts -- the per-header buf->ref and the per-data-block ref_count at the start of each variable/heap data allocation -- with plain non-atomic C operators (buf->ref++, if (--buf->ref > 0), if (--(*ref_count))). The API is documented as self-synchronizing: callers may share one buffer across threads (e.g. via k_fifo) and each holder independently calls net_buf_unref() with no surrounding lock. Under true concurrency (SMP, or single-core preemption between the non-atomic load and store while another context unrefs the same buffer), two holders can both observe the same prior reference value and both conclude they are the last reference. For heap/variable-data pools (mem_pool_data_unref/heap_data_unref, used by zbus message subscribers, the IP stack RX/TX buffers when CONFIG_NET_BUF_FIXED_DATA_SIZE=n, capture, wireguard, ISO-TP and usbip) this produces a double k_heap_free()/k_free() of the same block -- heap-metadata corruption and a use-after-free on the heap-hardening poison pattern. For the per-header refcount the buffer is returned to the pool free LIFO twice for any pool type (including fixed-data pools used by Bluetooth and networking), corrupting the free list so a later allocation hands the same buffer to two owners. The fix converts both refcounts to atomic_inc/atomic_dec (overlaying buf->ref in an atomic_t-sized union and changing the data-block refcount from uint8_t to atomic_t). Impact is gated on genuine concurrency and on an application architecture that shares one buffer among multiple independent unref'ers; the trigger is a refcount/timing race rather than packet content, so an external attacker has at most weak indirect influence over the race window. Affects all Zephyr releases through v4.4.0. This fix is not being backported to v3.7-branch (LTS). The backport was attempted and closed unmerged (#111181): the v3.7 networking tree has diverged from main, and the new atomic word-packing -- together with the assertions it adds -- turns pre-existing v3.7-only reference-counting defects elsewhere in the stack into hard faults, so landing the change faithfully would mean pulling an open-ended set of additional v3.7-only fixes into an LTS branch. v3.7 remains affected. Applications on v3.7 that share one net_buf across threads should serialize their own net_buf_unref() calls rather than rely on the documented self-synchronizing behaviour. The fix is on main and has been backported to v4.3-branch (#110852) and v4.4-branch (#110853).

References

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