CVE-2026-89718

None

CVSS

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EPSS

0.2%

Published

Sep 11, 2026

CISA due date

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Cloudanix analysis

Next patch cycle SSVC: Track

A timing flaw in Linux compressed memory handling could let a local attacker corrupt kernel memory or crash the system when the storage device is resized, though such attacks are difficult to carry out.

Exploitation: Local Privilege
Attacker needs: Local User
Complexity: Moderate
Impact: Privilege Gain
Component: OS kernel
Class: Race Condition
Remediation: Patch
Effort: Medium
Patch risk: Low

What it actually does

Race condition in zram writeback_store() derives table scan bounds from disksize before acquiring dev_lock; a concurrent reset and smaller reinitialization replaces the table, causing the scan to use stale bounds and perform out-of-bounds slot accesses on the new table.

Why it matters to the business

Systems relying on zram for compressed swap or block storage face risk of kernel memory corruption or crashes during device reconfiguration, potentially affecting availability and stability on Linux servers and embedded devices, though exploitation remains unlikely.

How an attack unfolds

An attacker with local access triggers a zram device reset followed by reinitialization to a smaller disksize while a concurrent writeback_store() call is blocked on dev_lock; once the lock is acquired the function scans using the old bound against the new table, resulting in out-of-bounds access.

How to fix it

Apply the upstream kernel patch that moves scan-bound calculations inside the dev_lock critical section; rebuild and deploy the fixed kernel across affected distributions; reboot systems after installation.

How to confirm the fix worked

Verify the patched source contains bound calculations performed while holding dev_lock in writeback_store(); inspect kernel logs after simulated reset/reconfigure sequences for absence of oops or slab corruption related to zram table scans.

Typical attack path

Obtain local code execution or shell on target Linux system
Reset an active zram device
Reconfigure the device with a smaller disksize
Trigger concurrent writeback operations that block on dev_lock
Exploit resulting out-of-bounds memory access

How to detect it

Search kernel logs and crash dumps for oops or BUG reports referencing writeback_store, zram table scans, or out-of-bounds accesses immediately following device reset or reinitialization events.

What your security team should do

Prioritize kernel updates on any systems using zram for swap or block storage
Monitor vendor advisories for backported fixes in supported LTS kernels
Limit untrusted local user access on systems where zram reconfiguration occurs

The record

In the Linux kernel, the following vulnerability has been resolved: zram: fix out-of-bounds access in writeback_store() Patch series "zram: fix stale scan bounds after reinitialization". Both writeback_store() and read_block_state() derive their table scan bounds from zram->disksize before acquiring dev_lock. If the device is reset and reinitialized with a smaller disksize between that read and lock acquisition, the bound can describe the old table while the scan operates on the new one. This can lead to out-of-bounds slot accesses. Move both bound calculations under dev_lock so each bound remains consistent with the table throughout its scan. Keep the fixes separate because the affected interfaces originate from different commits and can be backported independently. This patch (of 2): writeback_store() calculates the table scan bounds before taking dev_lock. A reset followed by reconfiguration with a smaller disksize can therefore replace zram->table while writeback_store() is waiting for the lock. Once it acquires the lock, it sees an initialized device but scans the new table using the old upper bound, resulting in an out-of-bounds access. Calculate the number of pages while holding dev_lock so the scan bound matches the table protected by the lock.

Affected packages

Ecosystem	Package	Introduced	Fixed