NVD / CVE Program· CNA XEN

CVE-2021-28691: Guest triggered use-after-free in Linux xen-netback A malicious or buggy network PV frontend can force Linux netback to disable the…

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: 0.36% (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 (Debian:12) 5.10.46-1.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to linux (Debian:12) 5.10.46-1 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

Guest triggered use-after-free in Linux xen-netback A malicious or buggy network PV frontend can force Linux netback to disable the interface and terminate the receive kernel thread associated with queue 0 in response to the frontend sending a malformed packet. Such kernel thread termination will lead to a use-after-free in Linux netback when the backend is destroyed, as the kernel thread associated with queue 0 will have already exited and thus the call to kthread_stop will be performed against a stale pointer.

Memory safety

BDU:2021-03230

Published: Jun 29, 2021
Updated: Aug 26, 2026
EPSS: 0.3% · 30th 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 · 0.3%

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

If any of these changes, we'll tell you in the daily email digest.

Is your version affected? Check it

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.

We use this product, ask for help

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
netapp	solidfire baseboard management controller	cpe:2.3:a:netapp:solidfire_baseboard_management_controller
netapp	cloud backup	cpe:2.3:a:netapp:cloud_backup
netapp	h410c firmware	cpe:2.3:o:netapp:h410c_firmware
netapp	h410c	cpe:2.3:h:netapp:h410c
netapp	h300s firmware	cpe:2.3:o:netapp:h300s_firmware
netapp	h300s	cpe:2.3:h:netapp:h300s
netapp	h500s firmware	cpe:2.3:o:netapp:h500s_firmware
netapp	h500s	cpe:2.3:h:netapp:h500s
netapp	h700s firmware	cpe:2.3:o:netapp:h700s_firmware
netapp	h700s	cpe:2.3:h:netapp:h700s
netapp	h300e firmware	cpe:2.3:o:netapp:h300e_firmware

and 7 more

Versions reported by the vendor

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

Linux Linux
- unspecified and later · before 4.12unknown
- 5.5.0 and later · before unspecifiedaffected
- next of 5.12.2 and later · before unspecifiednot affected

Affected versions · NVD (11)

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

linux linux kernel5.5.0 and later · before 5.10.43
netapp cloud backupall versions
netapp h300e firmwareall versions
netapp h300s firmwareall versions
netapp h410c firmwareall versions
netapp h410s firmwareall versions
netapp h500e firmwareall versions
netapp h500s firmwareall versions
netapp h700e firmwareall versions
netapp h700s firmwareall versions
netapp solidfire baseboard management controllerall versions

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 5.10.46-1	5.10.46-1

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-2020-28097Jun 24, 2021 · The vgacon subsystem in the Linux kernel before 5.8.10 mishandles software scrollback.
23Monitor
← EarlierCVE-2021-29703Jun 24, 2021 · Db2 for Linux, UNIX and Windows (includes Db2 Connect Server) is vulnerable to a denial of service as the server terminates abnormally when…
31Monitor
Later →CVE-2021-35039Jul 6, 2021 · kernel/module.c in the Linux kernel before 5.12.14 mishandles Signature Verification, aka CID-0c18f29aae7c.
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
debian:linux	5.10.46-1 · 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.

Credits

All researchers

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

Michael BrowniPXE and diagnosed by\nOlivier Benjamin, Michael Kurth and Martin Mazein o

National notice (Türkiye Cybersecurity Directorate / USOM)

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

TR-24-0205 · Mar 20, 2024(Linux Kernel Güncellemesi)

All national notices →

Not on record for this CVE: EPSS history · patch commit or PR link · 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, 10:48 PM UTC

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

References

security.gentoo.org/glsa/202107-30

Show all references (2 more)

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

All records