CVE-2025-21975

Kernel crash via unchecked mlx5 namespace lookup

Published Apr 1, 2025 · Updated May 11, 2026

NULL pointer dereference in the Linux kernel mlx5 flow-steering code allows local users to crash the system during flow-rule setup. mlx5_chains_create_table() dereferences a failed namespace lookup because it does not check error returns from mlx5_get_fdb_sub_ns() or mlx5_get_flow_namespace(). Reaching the path requires CAP_NET_ADMIN in the initial user namespace and TC offload or eswitch flow rules on a physical mlx5 device; the reported consequence is a kernel crash.

CVSS severity5.5
Medium
EPSS probability0.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

NULL pointer dereference in the Linux kernel mlx5 flow-steering code allows local users to crash the system during flow-rule setup. mlx5_chains_create_table() dereferences a failed namespace lookup because it does not check error returns from mlx5_get_fdb_sub_ns() or mlx5_get_flow_namespace(). Reaching the path requires CAP_NET_ADMIN in the initial user namespace and TC offload or eswitch flow rules on a physical mlx5 device; the reported consequence is a kernel crash.

The record

CVE
CVE-2025-21975
Published
Apr 1, 2025
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-476, T1499.004
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Apr 1, 2025CVE publishedPublication date reported by the CVE source.
  2. May 11, 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=39ac237ce00968545e7298faa9e07ecb7e440fb5 <093b4aaec97ec048623e3fe1e516fc45a954d412
  2. Affected versionversion=39ac237ce00968545e7298faa9e07ecb7e440fb5 <1598307c914ba3d2642a2b03d1ff11efbdb7c6c2
  3. Affected versionversion=39ac237ce00968545e7298faa9e07ecb7e440fb5 <15bdd93728369b2c8942a8e5d549d4b5dc04a2d9
  4. Affected versionversion=39ac237ce00968545e7298faa9e07ecb7e440fb5 <1d34296409a519b4027750e3e82d9e19553a7398
  5. Affected versionversion=39ac237ce00968545e7298faa9e07ecb7e440fb5 <29c419c64e9b396baeda1d8713d2aa3ba7c0acf6
  6. Affected versionversion=39ac237ce00968545e7298faa9e07ecb7e440fb5 <637105ef0d46fe5beac15aceb431da3ec832bb00
  7. Affected versionversion=39ac237ce00968545e7298faa9e07ecb7e440fb5 <eab0396353be1c778eba1c0b5180176f04dd21ce
  8. Affected versionversion=5.6

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

The Linux Kernel Organization · Linuxversion=39ac237ce00968545e7298faa9e07ecb7e440fb5 <093b4aaec97ec048623e3fe1e516fc45a954d412; version=39ac237ce00968545e7298faa9e07ecb7e440fb5 <1598307c914ba3d2642a2b03d1ff11efbdb7c6c2; version=39ac237ce00968545e7298faa9e07ecb7e440fb5 <15bdd93728369b2c8942a8e5d549d4b5dc04a2d9; version=39ac237ce00968545e7298faa9e07ecb7e440fb5 <1d34296409a519b4027750e3e82d9e19553a7398; version=39ac237ce00968545e7298faa9e07ecb7e440fb5 <29c419c64e9b396baeda1d8713d2aa3ba7c0acf6; version=39ac237ce00968545e7298faa9e07ecb7e440fb5 <637105ef0d46fe5beac15aceb431da3ec832bb00; version=39ac237ce00968545e7298faa9e07ecb7e440fb5 <eab0396353be1c778eba1c0b5180176f04dd21ce; version=5.6

Published CVSS scores

5.5Canonical UbuntuCVSS: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

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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)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
T1499.004Application or System Exploitation

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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