CVE-2021-47036

Service interruption via incorrect UDP tunnel aggregation

Published Feb 28, 2024 · Updated Aug 5, 2026

Incorrect UDP aggregation in Linux 5.6 through 5.12.3 allows local users to corrupt tunneled traffic and interrupt service. udp_gro_receive() applies SKB_GSO_UDP_L4 or SKB_GSO_FRAGLIST at the outer UDP layer, merging packets without respecting inner VXLAN identifiers or headers. Reachability requires enabled NETIF_F_GRO_FRAGLIST or NETIF_F_GRO_UDP_FWD and an available UDP tunnel; affected TCP packets can remain held until a GRO flush.

CVSS severity5.5
Medium
EPSS probability0.53%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect UDP aggregation in Linux 5.6 through 5.12.3 allows local users to corrupt tunneled traffic and interrupt service. udp_gro_receive() applies SKB_GSO_UDP_L4 or SKB_GSO_FRAGLIST at the outer UDP layer, merging packets without respecting inner VXLAN identifiers or headers. Reachability requires enabled NETIF_F_GRO_FRAGLIST or NETIF_F_GRO_UDP_FWD and an available UDP tunnel; affected TCP packets can remain held until a GRO flush.

The record

CVE
CVE-2021-47036
Published
Feb 28, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 28, 2024CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=5.6
  2. Affected versionversion=9fd1ff5d2ac7181844735806b0a703c942365291 <18f25dc399901426dff61e676ba603ff52c666f7
  3. Affected versionversion=9fd1ff5d2ac7181844735806b0a703c942365291 <450687386cd16d081b58cd7a342acff370a96078

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.6; version=9fd1ff5d2ac7181844735806b0a703c942365291 <18f25dc399901426dff61e676ba603ff52c666f7; version=9fd1ff5d2ac7181844735806b0a703c942365291 <450687386cd16d081b58cd7a342acff370a96078

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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