CVE-2025-21881Public exploit

System crash via shared-zeropage refcount underflow

Published Mar 27, 2025 · Updated May 11, 2026

Memory-management corruption in Linux kernel uprobes allows local users to crash the system through a BPF uprobe on a shared zeropage. mfill_atomic_pte_zeropage() maps the zero page without raising its RSS count or folio reference, after which uprobe_write_opcode() calls __replace_page() and unconditionally decrements both. The path requires local access to create the userfaultfd-backed mapping and attach a BPF multi-uprobe; successful triggering corrupts accounting and frees the reserved folio, producing a bad-page crash.

CVSS severityUnavailable
Unscored
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Memory-management corruption in Linux kernel uprobes allows local users to crash the system through a BPF uprobe on a shared zeropage. mfill_atomic_pte_zeropage() maps the zero page without raising its RSS count or folio reference, after which uprobe_write_opcode() calls __replace_page() and unconditionally decrements both. The path requires local access to create the userfaultfd-backed mapping and attach a BPF multi-uprobe; successful triggering corrupts accounting and frees the reserved folio, producing a bad-page crash.

The record

CVE
CVE-2025-21881
Published
Mar 27, 2025
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
Unavailable
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 27, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=2b144498350860b6ee9dc57ff27a93ad488de5dc <0b6f19714588cf2366b0364234f97ba963688f63
  2. Affected versionversion=2b144498350860b6ee9dc57ff27a93ad488de5dc <13cca2b73e2b0ec3ea6d6615d615395621d22752
  3. Affected versionversion=2b144498350860b6ee9dc57ff27a93ad488de5dc <54011fc94422f094eaf47555284de70a4bc32bb9
  4. Affected versionversion=2b144498350860b6ee9dc57ff27a93ad488de5dc <bddf10d26e6e5114e7415a0e442ec6f51a559468
  5. Affected versionversion=2b144498350860b6ee9dc57ff27a93ad488de5dc <c4cb2bfa99513311886c1eb5c1c2ac26f3338a6e
  6. Affected versionversion=3.5

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=2b144498350860b6ee9dc57ff27a93ad488de5dc <0b6f19714588cf2366b0364234f97ba963688f63; version=2b144498350860b6ee9dc57ff27a93ad488de5dc <13cca2b73e2b0ec3ea6d6615d615395621d22752; version=2b144498350860b6ee9dc57ff27a93ad488de5dc <54011fc94422f094eaf47555284de70a4bc32bb9; version=2b144498350860b6ee9dc57ff27a93ad488de5dc <bddf10d26e6e5114e7415a0e442ec6f51a559468; version=2b144498350860b6ee9dc57ff27a93ad488de5dc <c4cb2bfa99513311886c1eb5c1c2ac26f3338a6e; version=3.5

Published CVSS scores

No CVSS assessment is available in this record.

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 exploitPublished

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo