CVE-2026-39849: pi-hole ftl CRLF Injection

Vulnerability summary

CVE-2026-39849 is a high (CVSS 8.8) CRLF Injection vulnerability in pi-hole ftl. EPSS estimates a 1.00% chance of exploitation in the next 30 days, higher than 62.3% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 05-05-2026
   PublishedVulnerability first disclosed.
2. 08-05-2026
   Last modifiedVulnerability information updated.

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.

• CWE-93Improper Neutralization of CRLF Sequences ('CRLF Injection')The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.