Skip to main content
VulnerabilityPublished

CVE-2026-90834: zephyrproject zephyr · Memory-safety

Affects zephyrproject zephyrSource CVE Database V5

0
Compare

Not known to be exploited · CVSS 5.5 Medium : upgrade to 4.5.0 or 4.3.2 when convenient.

Data as of 10 Nov 2026, 22:19 UTC

CVSS 3.1 base score
5.5Medium
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (zephyr)CVSS 3.15.5
Patch
Available – fixed in 4.5.0, 4.3.2
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 10 Nov 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 10 Nov 2026.

What to do

Upgrade zephyrproject zephyr to 4.5.0 or 4.3.2.

Affected software

ProductAffectedFixed in
zephyrprojectzephyrAffected
  • >=4.4.0 <4.5.0
Fixed in
  • 4.5.0
zephyrprojectzephyrAffected
  • >=3.0.0 <4.3.2
Fixed in
  • 4.3.2
GitHubzephyrpkg:github/zephyrOther threatsAffected
  • >=3.0.0 <4.3.2
  • >=4.4.0 <4.5.0
Fixed in
  • 4.3.2
  • 4.5.0

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

Description

The user-mode syscall verifiers for the 16-bit ("wide data") UART API in drivers/serial/uart_handlers.c validated the wrong driver operation. z_vrfy_uart_poll_out_u16(), z_vrfy_uart_tx_u16() and z_vrfy_uart_rx_enable_u16() each ran K_SYSCALL_DRIVER_UART() against the 8-bit op (poll_out, tx, rx_enable) rather than the 16-bit op that the corresponding implementation dereferences (poll_out_u16, tx_u16, rx_enable_u16). z_impl_uart_poll_out_u16(), z_impl_uart_tx_u16() and z_impl_uart_rx_enable_u16() in include/zephyr/drivers/uart/uart_internal.h call their op unconditionally, with no NULL guard of their own, because the verifier is supposed to have established that the op exists. CONFIG_UART_WIDE_DATA is an application-selectable option that no driver selects, and only a handful of the serial drivers in the tree implement any _u16 operation; every other driver leaves those struct uart_driver_api members NULL while still providing the 8-bit ops the old check inspected. In a build with CONFIG_USERSPACE and CONFIG_UART_WIDE_DATA (plus CONFIG_UART_ASYNC_API for the uart_tx_u16() and uart_rx_enable_u16() variants), an unprivileged user-mode thread that legitimately holds access to such a UART device object can invoke the _u16 syscall: the object, permission and op checks all pass, and the kernel-side implementation then performs an indirect call through a NULL function pointer while running at supervisor privilege. The result is a CPU exception taken in kernel context instead of the intended K_OOPS or -ENOSYS return. With the default k_sys_fatal_error_handler() this halts the system (or warm-reboots it under CONFIG_RESET_ON_FATAL_ERROR), so a thread confined by the userspace sandbox can deny service to the whole device — a capability the user-mode privilege boundary is specifically meant to withhold. The call target is a fixed NULL, so there is no attacker-controlled code execution and no memory disclosure; the separate K_SYSCALL_MEMORY_ARRAY_READ()/K_SYSCALL_MEMORY_ARRAY_WRITE() bounds checks on the caller's buffer were and remain correct. The fix points each verifier at the matching _u16 op, using a plain K_SYSCALL_OBJ() object check where the op does not exist or where the implementation already tests it for NULL.

References

Community reviews

Loading reviews…