Linux · Linux Kernel · CVE-2021-47222
**Name of the Vulnerable Software and Affected Versions**
Linux kernel versions prior to 5.13.0-rc3+ #360
**Description**
The vulnerability is related to the egress tunnel code in the Linux kernel's bridge module. The code uses `dst clone()` and directly sets the result, which can cause problems if the entry has a reference count of 0 or has already been deleted. This triggers a `WARN ON()` in `dst hold()` when a reference count cannot be taken. The issue is fixed by using `dst hold safe()` and checking if a reference was actually taken before setting the destination.
**Recommendations**
To resolve the issue, update the Linux kernel to a version that includes the fix for the vulnerability. Specifically, for Linux kernel version 5.13.0-rc3+ #360, update to a newer version that includes the patch for the `net: bridge: fix vlan tunnel dst refcnt when egressing` vulnerability.
As a temporary workaround, consider disabling the vulnerable function or restricting access to the affected module to minimize the risk of exploitation. However, this should not be considered a permanent solution, and updating the kernel to a patched version is recommended as soon as possible.
At the moment, there is no information about a newer version that contains a fix for this vulnerability, other than updating to a version after 5.13.0-rc3+ #360.