# CVE-2021-47506: linux: In the Linux kernel, the following vulnerability has been resolved:  nfsd: fix use-after-free due to delegation race...

CVE-2021-47506 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47506, released May 24, 2024. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2021-47506
- Priority: High
- CVSS: 7.8 (high)
- EPSS: 0.0078
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 24, 2024

## Description

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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.15.15-1 | [DEBIAN-CVE-2021-47506](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47506.md) | May 24, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.15.15-1 | [DEBIAN-CVE-2021-47506](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47506.md) | May 24, 2024 |
| Linux | linux Debian 14 | 5.15.15-1 | [DEBIAN-CVE-2021-47506](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47506.md) | May 24, 2024 |

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