CVE-2021-47506: Linux Kernel

High severity, CVSS 7.8. EPSS: 0.8% chance of exploitation in the next 30 days.

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix use-after-free due to delegation race A delegation break could arrive as soon as we've called vfs_setlease. A delegation break runs a callback which immediately (in nfsd4_cb_recall_prepare) adds the delegation to del_recall_lru. If we then exit nfs4_set_delegation without hashing the delegation, it will be freed as soon as the callback is done with it, without ever being removed from del_recall_lru. Symptoms show up later as use-after-free or list corruption warnings, usually in the laundromat thread. I suspect aba2072f4523 "nfsd: grant read delegations to clients holding writes" made this bug easier to hit, but I looked as far back as v3.0 and it looks to me it already had the same problem. So I'm not sure where the bug was introduced; it may have been there from the beginning.

Affected products

• Linux Linux Kernel: before 4.4.296 (fixed in 4.4.296); from 4.5, before 4.9.294 (fixed in 4.9.294); from 4.10, before 4.14.259 (fixed in 4.14.259); from 4.15, before 4.19.222 (fixed in 4.19.222); from 4.20, before 5.4.168 (fixed in 5.4.168); from 5.5, before 5.10.85 (fixed in 5.10.85); …

Published 2024-05-24. Last modified 2026-08-04.