CVE-2026-10642: The Zephyr PL011 UART driver (drivers/serial/uart_pl011.c) contains an unbounded software loop in pl011_irq_tx_enable() that repeatedly invokes the in...

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.

Metrics

CVSS 3.1

4.6/10

CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

0.18%

8.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Zephyrproject	Zephyr	>= 4.1.0, < 4.5.0

References

https://github.com/zephyrproject-rtos/zephyr/commit/68e702294b711eadfe7b4fadedd46d7c87fe8f3dPatch
https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-3fgh-73jh-2q5jExploit, Patch, Vendor Advisory

Timeline

Published: Jun 24, 2026
Last Modified: Jul 14, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2026-10642?

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.

How severe is CVE-2026-10642?

CVE-2026-10642 has a CVSS score of 4.6/10 (MEDIUM severity). The EPSS model estimates a 0.18% probability of exploitation in the next 30 days.

How do I fix CVE-2026-10642?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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