A flaw in the Linux 8250 serial driver prevents the DMA transmission flag from being cleared when a DMA operation is cancelled and its completion callback does not run. The flag remains set and subsequent DMA transmit requests are blocked, causing the UART port to hang. This defect does not grant privilege escalation or remote code execution; it merely disrupts serial output, which can impact management, diagnostics, or boot processes that rely on UART communication.

The affected product is the Linux kernel’s 8250 UART serial driver. No specific kernel version ranges are enumerated, so any kernel build containing the driver before the patch that clears the TX flag is potentially vulnerable. The fix is present in the mainline kernel repository and is referenced by several commit URLs. Administrators should verify that their running kernel includes the commit sequence that implements the clearing of the DMA running flag or consider upgrading to a patched kernel.

The vulnerability requires a local or privileged user to trigger a DMA cancellation on an UART device, so the attack surface is limited to physical or compromised systems with control over the serial driver. There is no publicly reported exploitation and the EPSS score is unavailable, indicating low likelihood of exploitation. The impact is service disruption rather than data compromise. Because the defect is confined to UART instances using DMA, the risk is moderate: an attacker could cause a denial of service but would not gain further privileges or exfiltrate data. The vulnerability is not listed in CISA’s KEV catalog.