CVE-2025-21836

Privilege escalation via reused io_uring buffer list

Published Mar 7, 2025 · Updated Aug 5, 2026

Use-after-free in affected Linux kernel releases starting with 5.19 allows local users to read and write kernel memory through io_uring. IORING_REGISTER_PBUF_RING reuses an emptied legacy io_buffer_list, then exposes stale user mappings when the list is upgraded instead of allocating a fresh structure. An unprivileged local process can drive the registration sequence without user interaction, gaining arbitrary kernel reads and writes that enable privilege escalation or a kernel crash.

CVSS severity7.8
High
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in affected Linux kernel releases starting with 5.19 allows local users to read and write kernel memory through io_uring. IORING_REGISTER_PBUF_RING reuses an emptied legacy io_buffer_list, then exposes stale user mappings when the list is upgraded instead of allocating a fresh structure. An unprivileged local process can drive the registration sequence without user interaction, gaining arbitrary kernel reads and writes that enable privilege escalation or a kernel crash.

The record

CVE
CVE-2025-21836
Published
Mar 7, 2025
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 7, 2025CVE 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=2fcabce2d7d34f69a888146dab15b36a917f09d4 <146a185f6c05ee263db715f860620606303c4633
  2. Affected versionversion=2fcabce2d7d34f69a888146dab15b36a917f09d4 <2a5febbef40ce968e295a7aeaa5d5cbd9e3e5ad4
  3. Affected versionversion=2fcabce2d7d34f69a888146dab15b36a917f09d4 <7d0dc28dae836caf7645fef62a10befc624dd17b
  4. Affected versionversion=2fcabce2d7d34f69a888146dab15b36a917f09d4 <8802766324e1f5d414a81ac43365c20142e85603
  5. Affected versionversion=5.19

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=2fcabce2d7d34f69a888146dab15b36a917f09d4 <146a185f6c05ee263db715f860620606303c4633; version=2fcabce2d7d34f69a888146dab15b36a917f09d4 <2a5febbef40ce968e295a7aeaa5d5cbd9e3e5ad4; version=2fcabce2d7d34f69a888146dab15b36a917f09d4 <7d0dc28dae836caf7645fef62a10befc624dd17b; version=2fcabce2d7d34f69a888146dab15b36a917f09d4 <8802766324e1f5d414a81ac43365c20142e85603; version=5.19

Published CVSS scores

7.8LinuxCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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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

T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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