CVE-2021-47136Network attack vector

Forwarding disruption via uninitialized TC_SKB_EXT fields

Published Mar 25, 2024 · Updated Aug 5, 2026

Uninitialized memory use in Linux allows remote attackers to disrupt OVS forwarding via crafted traffic to affected mlx5 deployments. skb_ext_add() allocates TC_SKB_EXT without clearing it, while mlx5 restore paths initialize only chain and OVS later consumes stale mru and post_ct fields. When OVS uses mlx5 TC hardware offload, unauthenticated ingress traffic can expose bounded heap metadata, misclassify packets, or sustain flow drops.

CVSS severity5.5
Medium
EPSS probability0.54%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uninitialized memory use in Linux allows remote attackers to disrupt OVS forwarding via crafted traffic to affected mlx5 deployments. skb_ext_add() allocates TC_SKB_EXT without clearing it, while mlx5 restore paths initialize only chain and OVS later consumes stale mru and post_ct fields. When OVS uses mlx5 TC hardware offload, unauthenticated ingress traffic can expose bounded heap metadata, misclassify packets, or sustain flow drops.

The record

CVE
CVE-2021-47136
Published
Mar 25, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-908, T1498
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 25, 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=038ebb1a713d114d54dbf14868a73181c0c92758 <86ab133b695ed7ba1f8786b12f4ca43137ad8c18
  2. Affected versionversion=038ebb1a713d114d54dbf14868a73181c0c92758 <9453d45ecb6c2199d72e73c993e9d98677a2801b
  3. Affected versionversion=038ebb1a713d114d54dbf14868a73181c0c92758 <ac493452e937b8939eaf2d24cac51a4804b6c20e
  4. Affected versionversion=5.7.15 <5.8
  5. Affected versionversion=5.9
  6. Affected versionversion=7154bda4cfc1f41b339121475d2b0234141f3492

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=038ebb1a713d114d54dbf14868a73181c0c92758 <86ab133b695ed7ba1f8786b12f4ca43137ad8c18; version=038ebb1a713d114d54dbf14868a73181c0c92758 <9453d45ecb6c2199d72e73c993e9d98677a2801b; version=038ebb1a713d114d54dbf14868a73181c0c92758 <ac493452e937b8939eaf2d24cac51a4804b6c20e; version=5.7.15 <5.8; version=5.9; version=7154bda4cfc1f41b339121475d2b0234141f3492

Published CVSS scores

8.6Linux Kernel CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
5.5NIST National Vulnerability DatabaseCVSS: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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-908Use of Uninitialized Resource
T1498Network 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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