# CVE-2026-72840: OpenWrt LuCI luci-mod-system-mounts ACL Root RCE via Crontab Write

> Authenticated users with mount permissions can write to root crontab, achieving root code execution via the default cron daemon.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 13 Aug 2026
- **Updated:** 30 Sep 2026
- **Also known as:** GHSA-6vfc-74mf-qrmj

## What is CVE-2026-72840?

CVE-2026-72840 is a high-severity vulnerability in openwrt luci, published on 13 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

OpenWrt LuCI contains an overly permissive ACL definition in luci-mod-system-mounts that grants write access to /etc/crontabs/root to users intended only for mount configuration. Authenticated users with only the mount-configuration ACL group can append arbitrary cron entries via ubus file.write, which the default busybox crond daemon executes as root within one minute.

Weakness: CWE-266 (Incorrect Privilege Assignment)

## Which versions are affected by CVE-2026-72840?


## How do I fix CVE-2026-72840?

No fix has been published for CVE-2026-72840 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-72840 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-72840 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72840 and fix it if it is affected.

What it is: CVE-2026-72840 is a high-severity vulnerability in openwrt luci, published on 13 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-72840 exists.

Affected product: openwrt luci. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-72840/ (Markdown: https://insights.sbomify.com/CVE-2026-72840/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72840
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72840
- OSV: https://osv.dev/vulnerability/CVE-2026-72840

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72840/
Summaries are generated and may contain mistakes; the official description above is the record.