Vulnerability in Kernel (CVE-2025-40072)

Summary

Vulnerability in Kernel (CVE-2025-40072). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 6.17.3 or later.

Original description

The description as published by the source.

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

fanotify: Validate the return value of mnt_ns_from_dentry() before dereferencing

The function do_fanotify_mark() does not validate if
mnt_ns_from_dentry() returns NULL before dereferencing mntns->user_ns.
This causes a NULL pointer dereference in do_fanotify_mark() if the
path is not a mount namespace object.

Fix this by checking mnt_ns_from_dentry()'s return value before
dereferencing it.

Before the patch

$ gcc fanotify_nullptr.c -o fanotify_nullptr
$ mkdir A
$ ./fanotify_nullptr
Fanotify fd: 3
fanotify_mark: Operation not permitted
$ unshare -Urm
Fanotify fd: 3
Killed

int main(void){
int ffd;
ffd = fanotify_init(FAN_CLASS_NOTIF | FAN_REPORT_MNT, 0);
if(ffd < 0){
perror("fanotify_init");
exit(EXIT_FAILURE);
}

printf("Fanotify fd: %d\n",ffd);

if(fanotify_mark(ffd, FAN_MARK_ADD | FAN_MARK_MNTNS,

FAN_MNT_ATTACH, AT_FDCWD, "A") < 0){
perror("fanotify_mark");
exit(EXIT_FAILURE);
}

return 0;
}

After the patch

$ gcc fanotify_nullptr.c -o fanotify_nullptr
$ mkdir A
$ ./fanotify_nullptr
Fanotify fd: 3
fanotify_mark: Operation not permitted
$ unshare -Urm
Fanotify fd: 3
fanotify_mark: Invalid argument

[ 25.694973] BUG: kernel NULL pointer dereference, address: 0000000000000038
[ 25.695006] #PF: supervisor read access in kernel mode
[ 25.695012] #PF: error_code(0x0000) - not-present page
[ 25.695017] PGD 109a30067 P4D 109a30067 PUD 142b4606…

Source: OSV.dev (Open Source Vulnerabilities) NVD OSV

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-2025-40072 has been found in Kernel.
Risk of unauthorized operations or information disclosure.
What to do: upgrade Kernel to 6.17.3 or later.
If unsure, ask your IT team or search "Kernel CVE-2025-40072" on the vendor's site.

CVE-2025-40072 (Kernel)
Patched: 6.17.3 — apply immediately
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

A vulnerability (unclassified) exists in Kernel.

📍 Affected scope

Check the vendor advisory for the affected versions of Kernel.

🔥 Severity

Severity: ?. Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 6.17.3.

🛡️ 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. Run grep -r 'Kernel' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

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

1
Identify exposure identify
```
grep -r 'Kernel' . | grep -v node_modules
```
リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で Kernel を grep し、稼働しているサービス・バージョンを把握する。
2
Apply patch patch
```
Upgrade Kernel to 6.17.3
```
ステージング環境で 6.17.3 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
3
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":"6.16.0"},{"fixed":"6.17.3"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

BellSoft Alpaquita BELL-CVE-2025-40072 linux-lts Fixed in: 6.18.35-r1
Debian DEBIAN-CVE-2025-40072 linux Fixed in: 6.17.6-1
Ubuntu UBUNTU-CVE-2025-40072 linux-hwe-edge