CVE-2025-21671

Kernel memory access via dangling zram table

Published Jan 31, 2025 · Updated May 11, 2026

Use-after-free in the Linux zram driver allows local users to access freed kernel memory by resetting a failed, uninitialized device. When zram_meta_alloc fails early, it frees zram->table without clearing the pointer, and zram_meta_free later dereferences that stale allocation. Low-privileged local access and a failed, uninitialized zram device are required; the advisory does not document a demonstrated crash, disclosure, or privilege escalation.

CVSS severity7.8
High
EPSS probability0.22%
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 the Linux zram driver allows local users to access freed kernel memory by resetting a failed, uninitialized device. When zram_meta_alloc fails early, it frees zram->table without clearing the pointer, and zram_meta_free later dereferences that stale allocation. Low-privileged local access and a failed, uninitialized zram device are required; the advisory does not document a demonstrated crash, disclosure, or privilege escalation.

The record

CVE
CVE-2025-21671
Published
Jan 31, 2025
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-416
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 31, 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=0b5b0b65561b34e6e360de317e4bcd031bfabf42 <571d3f6045cd3a6d9f6aec33b678f3ffe97582ef
  2. Affected versionversion=6.1.122 <6.1.127
  3. Affected versionversion=6.12.7 <6.12.11
  4. Affected versionversion=6.6.68 <6.6.74
  5. Affected versionversion=6fb92e9a52e3feae309a213950f21dfcd1eb0b40 <902ef8f16d5ca77edc77c30656be54186c1e99b7
  6. Affected versionversion=74363ec674cb172d8856de25776c8f3103f05e2f <212fe1c0df4a150fb6298db2cfff267ceaba5402
  7. Affected versionversion=ac3b5366b9b7c9d97b606532ceab43d2329a22f3 <fe3de867f94819ba0f28e035c0b0182150147d95

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=0b5b0b65561b34e6e360de317e4bcd031bfabf42 <571d3f6045cd3a6d9f6aec33b678f3ffe97582ef; version=6.1.122 <6.1.127; version=6.12.7 <6.12.11; version=6.6.68 <6.6.74; version=6fb92e9a52e3feae309a213950f21dfcd1eb0b40 <902ef8f16d5ca77edc77c30656be54186c1e99b7; version=74363ec674cb172d8856de25776c8f3103f05e2f <212fe1c0df4a150fb6298db2cfff267ceaba5402; version=ac3b5366b9b7c9d97b606532ceab43d2329a22f3 <fe3de867f94819ba0f28e035c0b0182150147d95

Published CVSS scores

6.7Oracle LinuxCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
7.8UbuntuCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.8NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.8Amazon LinuxCVSS: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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free

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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