# CVE-2026-55159: luci-app-adblock-fast command injection in RPC cron entry

Source: https://junglewise.ai/threats/cve-2026-55159-luci-app-adblock-fast-a-webui-for-fast-lightweight-dns-based-ad  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-21. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-55159 · Severity: high · CVSS 8.8 · Published 2026-09-21

luci-app-adblock-fast is a web-based configuration tool for OpenWrt's DNS-based ad-blocking service. An authenticated user with write access can inject newline characters into cron job entries to create arbitrary additional root cron jobs, leading to command execution as the root user (UID 0) when the cron scheduler runs.

Vendors: [OpenWrt](https://junglewise.ai/threats/vendors/openwrt).

## Quick answers

**Is CVE-2026-55159 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-55159 being exploited in the wild.

**How severe is CVE-2026-55159?** High severity, with a CVSS score of 8.8, published 21 September 2026.

**Which products and versions are affected?** OpenWrt Luci-App-Adblock-Fast prior to 1.2.4-2.

**Is there a fix for CVE-2026-55159?** A patch was published on 2026-06-15. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-55159 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-55159?** Check whether you run OpenWrt Luci-App-Adblock-Fast at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The luci.adblock-fast.setCronEntry RPC method fails to sanitize carriage-return and line-feed characters in its entry parameter before writing to /etc/crontabs/root, allowing an authenticated attacker with the luci-app-adblock-fast write ACL to inject additional cron lines. The vulnerability requires authentication and the component-specific ACL permission, but not user interaction. The fix in 1.2.4-2 removes the vulnerable setCronEntry RPC and replaces it with syncCron, which validates schedule fields as bounded integers server-side.

## Affected products

- OpenWrt luci-app-adblock-fast prior to 1.2.4-2

## Timeline

- 2026-09-21: disclosed
- 2026-06-15: patched

## References

- [https://github.com/openwrt/luci/commit/9ccd99b5898457e5ef39dc21aea226d7fb6e5c7e](https://github.com/openwrt/luci/commit/9ccd99b5898457e5ef39dc21aea226d7fb6e5c7e)
- [https://github.com/openwrt/luci/commit/f67461fd0255bf992b2b559c22ec288067f2f9da](https://github.com/openwrt/luci/commit/f67461fd0255bf992b2b559c22ec288067f2f9da)