NVD / CVE Program· CNA Linux

CVE-2021-47505: aio: fix use-after-free due to missing POLLFREE handling

HighCVSS 7.8 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 31/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.25% (FIRST EPSS).
Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
Fixed version: Linux Linux 321fba81ec034f88aea4898993c1bf15605c023f, 4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f, 47ffefd88abfffe8a040bcc1dd0554d4ea6f7689.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 321fba81ec034f88aea4898993c1bf15605c023f, 4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f, 47ffefd88abfffe8a040bcc1dd0554d4ea6f7689 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: aio: fix use-after-free due to missing POLLFREE handling signalfd_poll() and binder_poll() are special in that they use a waitqueue whose lifetime is the current task, rather than the struct file as is normally the case. This is okay for blocking polls, since a blocking poll occurs within one task; however, non-blocking polls require another solution. This solution is for the queue to be cleared before it is freed, by sending a POLLFREE notification to all waiters. Unfortunately, only eventpoll handles POLLFREE. A second type of non-blocking poll, aio poll, was added in kernel v4.18, and it doesn't handle POLLFREE. This allows a use-after-free to occur if a signalfd or binder fd is polled with aio poll, and the waitqueue gets freed. Fix this by making aio poll handle POLLFREE. A patch by Ramji Jiyani <ramjiyani@google.com> (https://lore.kernel.org/r/20211027011834.2497484-1-ramjiyani@google.com) tried to do this by making aio_poll_wake() always complete the request inline if POLLFREE is seen. However, that solution had two bugs. First, it introduced a deadlock, as it unconditionally locked the aio context while holding the waitqueue lock, which inverts the normal locking order. Second, it didn't consider that POLLFREE notifications are missed while the request has been temporarily de-queued. The second problem was solved by my previous patch. This patch then properly fixes the use-after-free by handling POLLFREE in a deadlock-free way. It does this by taking advantage of the fact that freeing of the waitqueue is RCU-delayed, similar to what eventpoll does.

Memory safety

Published: May 24, 2024
Updated: Aug 5, 2026
EPSS: 0.2% · 16th percentile
CWE: CWE-416

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 31 / 40 · 7.8 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.2%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 7.8
CNA · Linux: 7.8; agree

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
linux	linux kernel	cpe:2.3:o:linux:linux_kernel

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

Linux Linux
- 4.18affected
- 2c14fa838cbefc23cf1c73ca167ed85b274b2913 and later · before 321fba81ec034f88aea4898993c1bf15605c023faffected · git
- 2c14fa838cbefc23cf1c73ca167ed85b274b2913 and later · before 4105e6a128e8a98455dfc9e6dbb2ab0c33c4497faffected · git
- 2c14fa838cbefc23cf1c73ca167ed85b274b2913 and later · before 47ffefd88abfffe8a040bcc1dd0554d4ea6f7689affected · git
- 2c14fa838cbefc23cf1c73ca167ed85b274b2913 and later · before 60d311f9e6381d779d7d53371f87285698ecee24affected · git
- 2c14fa838cbefc23cf1c73ca167ed85b274b2913 and later · before 50252e4b5e989ce64555c7aef7516bdefc2fea72affected · git
- before 4.18not affected · semver
- 4.19.221 and later · up to and including 4.19.*not affected · semver
- 5.4.165 and later · up to and including 5.4.*not affected · semver
- 5.10.85 and later · up to and including 5.10.*not affected · semver

Affected versions · NVD (5)

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

linux linux kernel4.18 and later · before 4.19.221
linux linux kernel4.20 and later · before 5.4.165
linux linux kernel5.5 and later · before 5.10.85
linux linux kernel5.11 and later · before 5.15.8
linux linux kernel5.16

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	linux	before 5.15.15-1	5.15.15-1
Red Hat:enterprise_linux:9::appstream	bpftool-debuginfo	before 0:7.4.0-503.11.1.el9_5	0:7.4.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-64k-debug-debuginfo	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-64k-debug-devel	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-64k-debug-devel-matched	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-64k-debuginfo	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-64k-devel	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-64k-devel-matched	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-debug-debuginfo	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-debug-devel	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-debug-devel-matched	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-debuginfo	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-debuginfo-common-aarch64	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-debuginfo-common-ppc64le	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-debuginfo-common-s390x	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-debuginfo-common-x86_64	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-devel	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-devel-matched	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-doc	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-headers	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-rt-debug-debuginfo	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-rt-debuginfo	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-tools-debuginfo	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5
Red Hat:enterprise_linux:9::appstream	kernel-zfcpdump-debuginfo	before 0:5.14.0-503.11.1.el9_5	0:5.14.0-503.11.1.el9_5

+58

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Published before and after this one in the same product

← EarlierCVE-2021-47502May 24, 2024 · ASoC: codecs: wcd934x: handle channel mappping list correctly
22Monitor
← EarlierCVE-2021-47503May 24, 2024 · scsi: pm80xx: Do not call scsi_remove_host() in pm8001_alloc()
24Monitor
Later →CVE-2021-47506May 24, 2024 · nfsd: fix use-after-free due to delegation race
31Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
Linux Linux	321fba81ec034f88aea4898993c1bf15605c023f	Vendor (CNA)
Linux Linux	4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f	Vendor (CNA)
Linux Linux	47ffefd88abfffe8a040bcc1dd0554d4ea6f7689	Vendor (CNA)
Linux Linux	50252e4b5e989ce64555c7aef7516bdefc2fea72	Vendor (CNA)
Linux Linux	60d311f9e6381d779d7d53371f87285698ecee24	Vendor (CNA)
debian:linux	5.15.15-1 · Debian:12	Package registry (OSV)
red hat:bpftool-debuginfo	0:7.4.0-503.11.1.el9_5 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)
red hat:kernel-64k-debug-debuginfo	0:5.14.0-503.11.1.el9_5 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)
red hat:kernel-64k-debug-devel	0:5.14.0-503.11.1.el9_5 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)
red hat:kernel-64k-debug-devel-matched	0:5.14.0-503.11.1.el9_5 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)
red hat:kernel-64k-debuginfo	0:5.14.0-503.11.1.el9_5 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)
red hat:kernel-64k-devel	0:5.14.0-503.11.1.el9_5 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)
red hat:kernel-64k-devel-matched	0:5.14.0-503.11.1.el9_5 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)
red hat:kernel-debug-debuginfo	0:5.14.0-503.11.1.el9_5 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)
red hat:kernel-debug-devel	0:5.14.0-503.11.1.el9_5 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)
red hat:kernel-debug-devel-matched	0:5.14.0-503.11.1.el9_5 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)
red hat:kernel-debuginfo	0:5.14.0-503.11.1.el9_5 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)
red hat:kernel-debuginfo-common-aarch64	0:5.14.0-503.11.1.el9_5 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

TR-24-0551 · May 27, 2024(Linux Kernel Güncellemesi)

All national notices →

Not on record for this CVE: EPSS history · patch commit or PR link · researcher credit · variant or chain candidate · public bounty program.

Technical details

Attack conditions

Someone with local access to the system can trigger it.
A low-privileged account is enough.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: high · data can be read
Integrity: high · data or configuration can be modified
Availability: high · the service can be disrupted

Attack vector: Local
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: High

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

nvd-primary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1free(dev->buf);
2/* ... another thread is still running ... */
3process(dev->buf);

Fixed

1lock(&dev->lock);
2free(dev->buf);
3dev->buf = NULL;
4unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log (1)

Fix✗ → ✓Sep 28, 2026, 10:09 PM UTC

For records you follow, these changes also arrive as notifications. →

References

git.kernel.org/stable/c/321fba81ec034f88aea4898993c1bf15605c023f

Show all references (4 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records