CVE-2021-47506

A flaw was found in the Linux kernel's Network File System daemon (nfsd). A race condition during delegation handling allows a delegation break callback to be processed before the delegation is properly registered and tracked. This causes the delegation memory structure to be freed while still referenced on the recall list, resulting in a use-after-free flaw. An attacker could exploit this vulnerability to cause memory corruption, potentially leading to a Denial of Service (DoS) or arbitrary code execution.

This flaw is rated as Moderate severity for Red Hat Enterprise Linux because exploitation requires winning a timing-dependent race condition on hosts explicitly deployed as NFS file servers, limiting broader exposure. By default, Red Hat Enterprise Linux installations do not enable or run the kernel NFS server daemon. Although memory corruption resulting in a kernel crash or system instability is possible, triggering the condition depends on concurrent delegation break operations that are difficult to induce reliably.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.