CVE-2021-47527

MEDIUM
Published May 24, 2024 Modified Sep 24, 2025 CWE-401

Description

In the Linux kernel, the following vulnerability has been resolved: serial: core: fix transmit-buffer reset and memleak Commit 761ed4a94582 ("tty: serial_core: convert uart_close to use tty_port_close") converted serial core to use tty_port_close() but failed to notice that the transmit buffer still needs to be freed on final close. Not freeing the transmit buffer means that the buffer is no longer cleared on next open so that any ioctl() waiting for the buffer to drain might wait indefinitely (e.g. on termios changes) or that stale data can end up being transmitted in case tx is restarted. Furthermore, the buffer of any port that has been opened would leak on driver unbind. Note that the port lock is held when clearing the buffer pointer due to the ldisc race worked around by commit a5ba1d95e46e ("uart: fix race between uart_put_char() and uart_shutdown()"). Also note that the tty-port shutdown() callback is not called for console ports so it is not strictly necessary to free the buffer page after releasing the lock (cf. d72402145ace ("tty/serial: do not free trasnmit buffer page under port lock")).

Is your site exposed to CVE-2021-47527?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

5.5
MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-401 CWE-401

Affected Products

Vendor Product
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel

References

Advisories & Patches

https://git.kernel.org/stable/c/00de977f9e0aa9760d9a79d1e41ff780f74e3424 https://git.kernel.org/stable/c/011f6c92b5bf6e1fbfdedc8b5232f64c1c493206 https://git.kernel.org/stable/c/1179b168fa3f3a6aae3bd140000455a0e58457db https://git.kernel.org/stable/c/64e491c1634b73d3bddc081d08620bdc92ab2c12 https://git.kernel.org/stable/c/c5da8aa441053958594f94254592bb41264bdfbf https://git.kernel.org/stable/c/e1722acf4f0d4d67b60f57e08ce16f8b66cd4b8f https://git.kernel.org/stable/c/e74d9663fd57640fc3394abb5c76fa95b9cc2f2e https://git.kernel.org/stable/c/00de977f9e0aa9760d9a79d1e41ff780f74e3424 https://git.kernel.org/stable/c/011f6c92b5bf6e1fbfdedc8b5232f64c1c493206 https://git.kernel.org/stable/c/1179b168fa3f3a6aae3bd140000455a0e58457db https://git.kernel.org/stable/c/64e491c1634b73d3bddc081d08620bdc92ab2c12 https://git.kernel.org/stable/c/c5da8aa441053958594f94254592bb41264bdfbf https://git.kernel.org/stable/c/e1722acf4f0d4d67b60f57e08ce16f8b66cd4b8f https://git.kernel.org/stable/c/e74d9663fd57640fc3394abb5c76fa95b9cc2f2e

Frequently Asked Questions

What is CVE-2021-47527? +
In the Linux kernel, the following vulnerability has been resolved: serial: core: fix transmit-buffer reset and memleak Commit 761ed4a94582 ("tty: serial_core: convert uart_close to use tty_port_close") converted serial core to use tty_port_close() but failed to notice that the transmit buffer still needs to be freed on final close. Not freeing the transmit buffer means that the buffer is no longer cleared on next open so that any ioctl() waiting for the buffer to drain might wait indefinitely (e.g. on termios changes) or that stale data can end up being transmitted in case tx is restarted. Furthermore, the buffer of any port that has been opened would leak on driver unbind. Note that the port lock is held when clearing the buffer pointer due to the ldisc race worked around by commit a5ba1d95e46e ("uart: fix race between uart_put_char() and uart_shutdown()"). Also note that the tty-port shutdown() callback is not called for console ports so it is not strictly necessary to free the buffer page after releasing the lock (cf. d72402145ace ("tty/serial: do not free trasnmit buffer page under port lock")). It has a CVSS v3.1 base score of 5.5 (MEDIUM).
How severe is CVE-2021-47527? +
CVE-2021-47527 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.
What products are affected by CVE-2021-47527? +
CVE-2021-47527 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.
How do I check if I'm vulnerable to CVE-2021-47527? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-0646

A denial-of-service security issue exists within the 1794-AENTR adapter due to improper memory handling of CIP protocol requests. This vulnerability …
CVE-2026-20746

Virtual attribute handling in Ping Identity PingDirectory in affected versions allows only authorized users to exhaust java memory heap when …
CVE-2026-53429

Missing Release of Memory after Effective Lifetime vulnerability in leandrocp mdex and mdex_native allows an attacker who controls a rendered …
CVE-2024-25450 8.8

imlib2 v1.9.1 was discovered to mishandle memory allocation in the function init_imlib_fonts().
CVE-2025-20133 8.6

A vulnerability in the management and VPN web servers of the Remote Access SSL VPN feature of Cisco Secure Firewall …
CVE-2025-20239 8.6

A vulnerability in the Internet Key Exchange Version 2 (IKEv2) feature of Cisco IOS Software, IOS XE Software, Secure Firewall …

Don't wait for an exploit

Scan your website for vulnerabilities like CVE-2021-47527 — free, no signup required.