Integer underflow in Linux kernel - CVE-2026-63883

Vulnerability identifier: #VU138766

CSH Severity: Low

CVSS v4: 4.8 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-63883

CWE-ID: CWE-191

Exploitation vector: Local access

Exploit availability: No public exploit available

The vulnerability allows a local user to disclose stale buffer data.

The vulnerability exists due to an integer underflow in qcom_geni_serial_handle_tx_dma() when handling a DMA completion interrupt after uart_flush_buffer() resets the transmit buffer. A local user can trigger a flush before DMA completion is processed to disclose stale buffer data.

The issue is caused by a race condition between transmit buffer flushing and delayed DMA completion handling.

Linux kernel
Ubuntu
linux-ibm (Ubuntu package)
linux-azure (Ubuntu package)
linux-aws (Ubuntu package)
linux-nvidia (Ubuntu package)
linux-nvidia-bos (Ubuntu package)

Install security update from vendor's repository.

Linux kernel - update to 7.0 rc3
linux-ibm (Ubuntu package) - addressed in versions 7.0.0-1008.8, 7.0.0-1010.10
linux-azure (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1010.10
linux-aws (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1015.15
linux-nvidia (Ubuntu package) - addressed in versions 7.0.0-1016.16, 7.0.0-1016.16~24.04.1
linux-nvidia-bos (Ubuntu package) - update to 7.0.0-2016.16

• https://git.kernel.org/stable/c/0d2c41a8b00934ddf8a7c1b4cf72dffa1e629c46
• https://git.kernel.org/stable/c/452d6fa37ae9b021f4f6d397dbae077f7296f6f4
• https://git.kernel.org/stable/c/654f45a8569f3cd6ff20bd724a18e0cce65893ba
• https://git.kernel.org/stable/c/b1159dce10b38eb795e4c96cdc4d34b83cec81c5
• https://git.kernel.org/stable/c/c91ea13375f70f6271a0183445e34e83b8f4d8f7

• Integer underflow in Linux kernel tty serial driver
• Ubuntu update for linux-ibm
• Ubuntu update for linux-azure
• Ubuntu update for linux-aws
• Ubuntu update for linux-nvidia-bos
• Ubuntu update for linux-nvidia