CVE-2026-39849: CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection') in pi-hole FTL
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.
AI Analysis
Technical Summary
CVE-2026-39849 is a CRLF injection vulnerability (CWE-93) in Pi-hole FTL prior to version 6.6.1. The dns.interface configuration field improperly accepts newline characters, allowing injection of arbitrary dnsmasq directives. Without an admin password, the configuration API is unauthenticated, enabling network-adjacent attackers to inject payloads that persist in /etc/pihole/pihole.toml and execute arbitrary commands on the host when DHCP leases are requested. The vulnerability arises because the validation in FTL 6.6 only checks syntactic validity and does not prevent newline injection. The issue is resolved in version 6.6.1.
Potential Impact
An attacker with network adjacency and access to the configuration API on Pi-hole FTL installations without an admin password can inject malicious directives into the dnsmasq configuration. This can lead to enabling the DHCP server and arbitrary command execution on the host system, potentially compromising the entire device running Pi-hole. The injected payload persists across restarts, increasing the risk of sustained compromise.
Mitigation Recommendations
This vulnerability is fixed in Pi-hole FTL version 6.6.1. Users should upgrade to version 6.6.1 or later to remediate this issue. Additionally, setting an admin password on the Pi-hole installation prevents unauthenticated access to the configuration API, mitigating the risk of exploitation. Patch status is not explicitly confirmed in the vendor advisory, but the fix is stated to be included in version 6.6.1.
CVE-2026-39849: CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection') in pi-hole FTL
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.
CVSS v4.0
Score 8.7high
Affected software
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-39849 is a CRLF injection vulnerability (CWE-93) in Pi-hole FTL prior to version 6.6.1. The dns.interface configuration field improperly accepts newline characters, allowing injection of arbitrary dnsmasq directives. Without an admin password, the configuration API is unauthenticated, enabling network-adjacent attackers to inject payloads that persist in /etc/pihole/pihole.toml and execute arbitrary commands on the host when DHCP leases are requested. The vulnerability arises because the validation in FTL 6.6 only checks syntactic validity and does not prevent newline injection. The issue is resolved in version 6.6.1.
Potential Impact
An attacker with network adjacency and access to the configuration API on Pi-hole FTL installations without an admin password can inject malicious directives into the dnsmasq configuration. This can lead to enabling the DHCP server and arbitrary command execution on the host system, potentially compromising the entire device running Pi-hole. The injected payload persists across restarts, increasing the risk of sustained compromise.
Mitigation Recommendations
This vulnerability is fixed in Pi-hole FTL version 6.6.1. Users should upgrade to version 6.6.1 or later to remediate this issue. Additionally, setting an admin password on the Pi-hole installation prevents unauthenticated access to the configuration API, mitigating the risk of exploitation. Patch status is not explicitly confirmed in the vendor advisory, but the fix is stated to be included in version 6.6.1.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-04-07T19:13:20.378Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 69fa5fd1cbff5d8610282e41
Added to database: 5/5/2026, 9:23:29 PM
Last enriched: 5/13/2026, 3:33:28 AM
Last updated: 6/20/2026, 7:33:58 AM
Views: 89
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