CVE-2026-10642 Unbounded TX busy-loop DoS in Zephyr PL011 UART driver under CTS hardware flow control
An attacker with adjacent access can cause a denial of service in Zephyr RTOS by withholding CTS signals during UART transmission, triggering an infinite loop.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-10642?
CVE-2026-10642 is a medium-severity denial of service vulnerability in Zephyrproject Zephyr, published on 24 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
The Zephyr PL011 UART driver (drivers/serial/uart_pl011.c) contains an unbounded software loop in pl011_irq_tx_enable() that repeatedly invokes the interrupt-driven application callback while the TX interrupt mask bit (PL011_IMSC_TXIM) is set, to work around the controller's level-transition TX-interrupt behavior.
When CTS hardware flow control is enabled (devicetree hw-flow-control or runtime UART_CFG_FLOW_CTRL_RTS_CTS) and the wired serial peer de-asserts CTS, the controller stops draining the TX FIFO; pl011_fifo_fill() then returns 0 on every call while the application still has pending data and therefore never disables the TX interrupt. The loop condition never clears, so the thread that called uart_irq_tx_enable() (e.g. h4_send() in the Bluetooth HCI H4 driver) spins indefinitely, hanging the executing context and stalling the transport — a denial of service (CWE-835).
An attacker controlling the device attached to the UART's CTS line can trigger the hang by withholding CTS during transmission. Because that peer is the device wired to the UART — which may be a removable or external module (e.g. an off-board Bluetooth controller on the HCI H4 link) rather than a permanently-bonded on-PCB part — the attack vector is scored Adjacent (AV:A) rather than Physical; the security subcommittee should confirm the vector against the specific deployment. Impact is availability only; there is no memory-safety, confidentiality, or integrity consequence.
The vulnerable loop was introduced in commit b783bc8448ef (Feb 2025) and shipped in releases v4.1.0 through v4.4.0. The fix breaks out of the loop when CTS is blocking and arms the CTS modem-status interrupt to resume transmission when CTS re-asserts.
Weakness: CWE-835
Which versions are affected by CVE-2026-10642?
It affects 1 product.
Products include Zephyrproject Zephyr.
How do I fix CVE-2026-10642?
No fix has been published for CVE-2026-10642 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-10642 being exploited?
There is no known exploitation of CVE-2026-10642 in the wild and no public exploit code.
Other vulnerabilities in Zephyrproject Zephyr
- CVE-2026-5067 Out-of-bounds read/write in HTTP WebSocket upgrade via non-null-terminated Sec-WebSocket-Key
- CVE-2022-3806 Bluetooth HCI Error Handling Double Free
- CVE-2017-14199 Memory corruption in getaddrinfo
- CVE-2018-1000800 Null dereference in n/a
- CVE-2021-3329 DOS: Incorrect handling of the initial HCI ACL_MTU handshake packet leads to crash of bluetooth host layer
Sources
Also known as GHSA-3fgh-73jh-2q5j.