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CVE-2021-47506

Disclosure Date: May 24, 2024 •
CVE-2021-47506
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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.

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CVSS V3 Severity and Metrics
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Impact Score:
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Exploitability Score:
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Vector:
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Attack Vector (AV):
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Attack Complexity (AC):
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Privileges Required (PR):
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User Interaction (UI):
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Confidentiality (C):
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Integrity (I):
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Availability (A):
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General Information

Offensive Application
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Utility Class
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Ports
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OS
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Vulnerable Versions
Linux 04a8d07f3d58
Linux not down converted
Prerequisites
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Discovered By
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PoC Author
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Metasploit Module
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Reporter
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Vendors

  • Linux

Products

  • Linux
Technical Analysis