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CVE-2021-47506

9.8 · CRITICAL

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.

Published May 24, 2024CWE-416EPSS 0.78%

Overview

CVE-2021-47506 is a critical-severity vulnerability. It was published on May 24, 2024 and has a CVSS 3.1 base score of 9.8 (CRITICAL).

This vulnerability has a CVSS 3.1 base score of 9.8, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refgit.kernel.org/stable/c/04a8d07f3d58308b92630045560799a3faa3ebceRefgit.kernel.org/stable/c/148c816f10fd11df27ca6a9b3238cdd42fa72cd3Refgit.kernel.org/stable/c/2becaa990b93cbd2928292c0b669d3abb6cf06d4Refgit.kernel.org/stable/c/33645d3e22720cac1e4548f8fef57bf0649536eeRefgit.kernel.org/stable/c/348714018139c39533c55661a0c7c990671396b4Refgit.kernel.org/stable/c/548ec0805c399c65ed66c6641be467f717833ab5Refgit.kernel.org/stable/c/e0759696de6851d7536efddfdd2dfed4c4df1f09Refgit.kernel.org/stable/c/eeb0711801f5e19ef654371b627682aed3b11373Refgit.kernel.org/stable/c/04a8d07f3d58308b92630045560799a3faa3ebceRefgit.kernel.org/stable/c/148c816f10fd11df27ca6a9b3238cdd42fa72cd3

How CyberStrike helps

Frequently asked questions

What is CVE-2021-47506?

CVE-2021-47506 is a critical-severity vulnerability. It was published on May 24, 2024 and has a CVSS 3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2021-47506?

This vulnerability has a CVSS 3.1 base score of 9.8, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2021-47506?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2021-47506?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-47506 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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