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CVE-2026-31703 high CVSS 7.8

Use-After-Free in Linux kernel (CVE-2026-31703)

Summary

Vulnerability in Linux kernel (CVE-2026-31703). Successful exploitation can lead to full system takeover.

Original description

The description as published by the source.

In the Linux kernel, the following vulnerability has been resolved:

writeback: Fix use after free in inode_switch_wbs_work_fn()

inode_switch_wbs_work_fn() has a loop like:

wb_get(new_wb);
while (1) {
list = llist_del_all(&new_wb->switch_wbs_ctxs);
/* Nothing to do? */
if (!list)
break;
... process the items ...
}

Now adding of items to the list looks like:

wb_queue_isw()
if (llist_add(&isw->list, &wb->switch_wbs_ctxs))
queue_work(isw_wq, &wb->switch_work);

Because inode_switch_wbs_work_fn() loops when processing isw items, it
can happen that wb->switch_work is pending while wb->switch_wbs_ctxs is
empty. This is a problem because in that case wb can get freed (no isw
items -> no wb reference) while the work is still pending causing
use-after-free issues.

We cannot just fix this by cancelling work when freeing wb because that
could still trigger problematic 0 -> 1 transitions on wb refcount due to
wb_get() in inode_switch_wbs_work_fn(). It could be all handled with
more careful code but that seems unnecessarily complex so let's avoid
that until it is proven that the looping actually brings practical
benefit. Just remove the loop from inode_switch_wbs_work_fn() instead.
That way when wb_queue_isw() queues work, we are guaranteed we have
added the first item to wb->switch_wbs_ctxs and nobody is going to
remove it (and drop the wb reference it holds) until the queued work
runs.

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-31703 has been found in Linux kernel.
Successful exploitation can lead to full system takeover. CVSS score: 7.8/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Linux kernel CVE-2026-31703" on the vendor's site.

CVE-2026-31703 (Linux kernel) — CWE-416 / CVSS v3 7.8
Attack vector: local / no user interaction
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Use-after-free (CWE-416) exists in Linux kernel.

📍 Affected scope

Check the vendor advisory for the affected versions of Linux kernel.

🔥 Severity

Severity: High (CVSS 7.8/10). Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to the patched release per vendor advisory.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    Audit SBOM/dependencies for affected components.

    資産台帳・SBOM・依存マニフェストで Linux kernel を使っているサービスとバージョンを洗い出す。

  2. 2
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

Linux Kernel
[{"type":"ECOSYSTEM","events":[{"introduced":"6.18.0"},{"fixed":"6.18.25"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.0.2"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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