CVE-2021-47527 is a vulnerability in the Linux kernel's serial core subsystem related to improper management of the transmit buffer during port closure. Specifically, a code change (commit 761ed4a94582) that converted the serial core to use tty_port_close() failed to free the transmit buffer on the final close of a serial port. This omission results in the transmit buffer not being cleared upon the next open, causing ioctl() calls that wait for the buffer to drain (such as those triggered by termios changes) to potentially hang indefinitely. Additionally, stale data may be transmitted if transmission is restarted without clearing the buffer. Another consequence is a memory leak occurring when a driver is unbound, as the buffer of any opened port is not freed. The vulnerability involves race conditions around port locking and buffer clearing, with some complexity due to console ports not invoking the tty-port shutdown callback. The issue was addressed by ensuring proper freeing of the transmit buffer outside the port lock after shutdown, preventing indefinite waits and memory leaks. This vulnerability affects Linux kernel versions including the commit 761ed4a94582ab291aa24dcbea4e01e8936488c8 and potentially other versions incorporating this change. No known exploits are reported in the wild, and no CVSS score has been assigned yet.

For European organizations relying on Linux-based systems, especially those using serial communication interfaces (e.g., embedded systems, industrial control systems, telecommunications equipment, and legacy hardware interfaces), this vulnerability can cause system instability and degraded service availability. The indefinite blocking of ioctl() calls waiting for buffer drainage can lead to application hangs or kernel-level resource starvation, impacting operational continuity. Memory leaks during driver unbind operations can degrade system performance over time, potentially leading to crashes or forced reboots. While the vulnerability does not directly enable privilege escalation or remote code execution, the denial of service conditions and data integrity issues (stale data transmission) can disrupt critical processes. Organizations operating industrial automation, manufacturing, or critical infrastructure in Europe that use Linux kernels with affected versions may face increased risk of operational disruption. The absence of known exploits suggests limited immediate threat, but the vulnerability's presence in widely deployed Linux kernels means that unpatched systems remain at risk of stability and reliability issues.

European organizations should prioritize updating Linux kernels to versions that include the fix for CVE-2021-47527. Kernel maintainers and distributors have addressed this issue by ensuring the transmit buffer is properly freed on port closure. System administrators should audit their environments to identify systems using affected kernel versions, particularly those with serial port drivers or embedded Linux devices. For embedded or specialized devices where kernel updates are challenging, consider implementing workarounds such as controlled port reopen sequences or monitoring for hung ioctl() calls to trigger automated recovery. Additionally, thorough testing of serial communication subsystems after patching is advised to confirm that buffer management behaves correctly and no regressions occur. Monitoring system logs for signs of memory leaks or serial port hangs can help detect exploitation or manifestation of the vulnerability. Finally, organizations should engage with hardware and software vendors to ensure timely patch deployment and consider network segmentation for critical Linux-based devices to limit exposure.