9.8

CVE-2021-47506: nfsd: fix use-after-free due to delegation race

Modified
AliasesUBUNTU-CVE-2021-47506DEBIAN-CVE-2021-47506
Published 24-05-2024Last modified 05-08-2026

Vulnerability summary

CVE-2021-47506 is a critical (CVSS 9.8) Use After Free vulnerability in linux. EPSS estimates a 0.78% chance of exploitation in the next 30 days, higher than 56% of scored vulnerabilities.

Priority
Prioritisesevere

Severe, CVSS 9.8 (CVE.org); no exploitation reported by the 5 checked sources; EPSS 1% (FIRST, 03-11-2026)

Source freshness unavailable

How is this decided?
CVSS score
9.8/10
010
Critical · v3.1 (CVE.org)
EPSS score
0.78%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 18 · Related 17
LSN-0112-1SUSE-SU-2024:1979-1SUSE-SU-2024:1983-1SUSE-SU-2024:2008-1SUSE-SU-2024:2010-1SUSE-SU-2024:2011-1

Timeline

  1. 24-05-2024
    PublishedVulnerability first disclosed.
  2. 05-08-2026
    Last modifiedVulnerability information updated.

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.

CVSS metrics

4 scores · 4 sources · 1 version

EPSS trend

Probability

0.78%

Chance of exploitation in the next 30 days

Percentile

56%

Versus all other CVEs

30-day change

No change 0.00 pp

From 0.78% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Ubuntu89 products
  • linuxAll versions (No fix recorded) | < 4.4.0-268.302 | < 4.15.0-169.177 | < 5.4.0-105.119
  • linux-allwinner-5.19All versions (No fix recorded)
  • linux-aws< 4.4.0-1143.149 | < 4.4.0-1181.196 | < 4.15.0-1121.129 | < 5.4.0-1069.73
  • linux-aws-5.0All versions (No fix recorded)
  • linux-aws-5.11All versions (No fix recorded)
Linux2 products
  • linux≥ dff1399f8addf7129c49bb2227469da79cc30b47, < 04a8d07f3d58308b92630045560799a3faa3ebce | ≥ dff1399f8addf7129c49bb2227469da79cc30b47, < 348714018139c39533c55661a0c7c990671396b4 | ≥ dff1399f8addf7129c49bb2227469da79cc30b47, < 33645d3e22720cac1e4548f8fef57bf0649536ee | ≥ dff1399f8addf7129c49bb2227469da79cc30b47, < 2becaa990b93cbd2928292c0b669d3abb6cf06d4 | ≥ dff1399f8addf7129c49bb2227469da79cc30b47, < e0759696de6851d7536efddfdd2dfed4c4df1f09 | ≥ dff1399f8addf7129c49bb2227469da79cc30b47, < eeb0711801f5e19ef654371b627682aed3b11373 | ≥ dff1399f8addf7129c49bb2227469da79cc30b47, < 148c816f10fd11df27ca6a9b3238cdd42fa72cd3 | ≥ dff1399f8addf7129c49bb2227469da79cc30b47, < 548ec0805c399c65ed66c6641be467f717833ab5 | 3.17
  • linux_kernel< 4.4.296 | ≥ 4.5, < 4.9.294 | ≥ 4.10, < 4.14.259 | ≥ 4.15, < 4.19.222 | ≥ 4.20, < 5.4.168 | ≥ 5.5, < 5.10.85 | ≥ 5.11, < 5.15.8 | 5.15:rc1 | 5.15:rc2 | 5.15:rc3 | 5.15:rc4
Debian1 product
  • linux< 5.15.15-1

3 vendors · 92 products

References

16 links
Show all 16 references