NVD / CVE Program· CNA Linux

CVE-2021-47355: atm: nicstar: Fix possible use-after-free in nicstar_cleanup()

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: 0.24% (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 2f958b6f6ba0854b39be748d21dfe71e0fe6580f, 34e7434ba4e97f4b85c1423a59b2922ba7dff2ea, 4e2a0848ea2cab0716d46f85a8ccd5fa9a493e51.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 2f958b6f6ba0854b39be748d21dfe71e0fe6580f, 34e7434ba4e97f4b85c1423a59b2922ba7dff2ea, 4e2a0848ea2cab0716d46f85a8ccd5fa9a493e51 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: atm: nicstar: Fix possible use-after-free in nicstar_cleanup() This module's remove path calls del_timer(). However, that function does not wait until the timer handler finishes. This means that the timer handler may still be running after the driver's remove function has finished, which would result in a use-after-free. Fix by calling del_timer_sync(), which makes sure the timer handler has finished, and unable to re-schedule itself.

HighCVSS 7.8 · v3.1—No exploit Fix available

Memory safety

BDU:2025-07457

Published: May 21, 2024
Updated: Jun 17, 2026
EPSS: 0.2% · 15th percentile
CWE: CWE-416

Report tools

JSON

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.

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

Affected versions

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

linux linux kernelbefore 4.4.276
linux linux kernel4.5 and later · before 4.9.276
linux linux kernel4.10 and later · before 4.14.240
linux linux kernel4.15 and later · before 4.19.198
linux linux kernel4.20 and later · before 5.4.133
linux linux kernel5.5 and later · before 5.10.51
linux linux kernel5.11 and later · before 5.12.18
linux linux kernel5.13 and later · before 5.13.3

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
- 2.6.12affected
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before 99779c9d9ffc7775da6f7fd8a7c93ac61657bed5affected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before 4e2a0848ea2cab0716d46f85a8ccd5fa9a493e51affected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before c471569632654e57c83512e0fc1ba0dbb4544ad6affected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before a7a7b2848312cc4c3a42b6e42a8ab2e441857abaaffected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before bdf5334250c69fabf555b7322c75249ea7d5f148affected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before a7f7c42e31157d1f0871d6a8e1a0b73a6b4ea785affected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before 2f958b6f6ba0854b39be748d21dfe71e0fe6580faffected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before 5b991df8881088448cb223e769e37cab8dd40706affected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before 34e7434ba4e97f4b85c1423a59b2922ba7dff2eaaffected · git

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 5.14.6-1	5.14.6-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
90Now
CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
89Now
CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
85Now

Published before and after this one in the same product

← EarlierCVE-2021-47353May 21, 2024 · udf: Fix NULL pointer dereference in udf_symlink function
22Monitor
← EarlierCVE-2021-47354May 21, 2024 · drm/sched: Avoid data corruptions
28Monitor
Later →CVE-2021-47356May 21, 2024 · mISDN: fix possible use-after-free in HFC_cleanup()
30Monitor

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	2f958b6f6ba0854b39be748d21dfe71e0fe6580f	Vendor (CNA)
Linux Linux	34e7434ba4e97f4b85c1423a59b2922ba7dff2ea	Vendor (CNA)
Linux Linux	4e2a0848ea2cab0716d46f85a8ccd5fa9a493e51	Vendor (CNA)
Linux Linux	5b991df8881088448cb223e769e37cab8dd40706	Vendor (CNA)
Linux Linux	99779c9d9ffc7775da6f7fd8a7c93ac61657bed5	Vendor (CNA)
Linux Linux	a7a7b2848312cc4c3a42b6e42a8ab2e441857aba	Vendor (CNA)
Linux Linux	a7f7c42e31157d1f0871d6a8e1a0b73a6b4ea785	Vendor (CNA)
Linux Linux	bdf5334250c69fabf555b7322c75249ea7d5f148	Vendor (CNA)
Linux Linux	c471569632654e57c83512e0fc1ba0dbb4544ad6	Vendor (CNA)
debian:linux	5.14.6-1 · Debian:12	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.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

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

TR-24-0519 · May 22, 2024(Linux Kernel Güncellemesi)

All national notices →

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

Fix✗ → ✓Sep 28, 2026, 10:09 PM UTC

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

References

git.kernel.org/stable/c/2f958b6f6ba0854b39be748d21dfe71e0fe6580f

Show all references (8 more)

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

All records