CVE-2026-41230 Overview
CVE-2026-41230 is a DNS record injection vulnerability affecting Froxlor, an open-source server administration software. The vulnerability exists in the DomainZones::add() function, which accepts arbitrary DNS record types without a whitelist and fails to sanitize newline characters in the content field. When a DNS record type not covered by the validation chain is submitted (such as NAPTR, PTR, or HINFO), content validation is entirely bypassed. This allows embedded newline characters to survive trim() processing, get stored in the database, and be written directly into BIND zone files via DnsEntry::__toString().
Critical Impact
An authenticated customer can inject arbitrary DNS records and BIND directives ($INCLUDE, $ORIGIN, $GENERATE) into their domain's zone file, potentially leading to DNS hijacking, cache poisoning, or service disruption across affected domains.
Affected Products
- Froxlor Server Administration Software versions prior to 2.3.6
Discovery Timeline
- 2026-04-23 - CVE CVE-2026-41230 published to NVD
- 2026-04-23 - Last updated in NVD database
Technical Details for CVE-2026-41230
Vulnerability Analysis
This vulnerability is classified under CWE-93 (Improper Neutralization of CRLF Sequences). The core issue lies in the incomplete validation logic within the DomainZones::add() function. The function uses an if/elseif validation chain to handle known DNS record types, but any record type not explicitly covered by this chain completely bypasses content validation.
The attack surface is accessible to authenticated customers through the domain zone management interface. When an attacker submits a DNS record type like NAPTR, PTR, or HINFO that falls outside the handled types, the content field passes through without proper sanitization. The trim() function used for processing does not strip embedded newline characters within the content string, only leading and trailing whitespace.
These unsanitized newline characters are then persisted to the database and subsequently written directly into BIND zone files through the DnsEntry::__toString() method. This allows attackers to inject arbitrary DNS records or BIND directives into zone files, which are then served by the DNS server.
Root Cause
The root cause is the absence of a DNS record type whitelist combined with insufficient input sanitization. The validation logic only handles a predefined set of record types, allowing unhandled types to bypass all content validation. Additionally, the content sanitization fails to remove or escape embedded newline characters (CRLF sequences), enabling injection attacks.
Attack Vector
This is a network-accessible vulnerability requiring low-privilege authentication (customer-level access). An attacker with a valid customer account can exploit this vulnerability through the Froxlor web interface by:
- Creating a new DNS record with an unhandled record type (e.g., NAPTR, PTR, HINFO)
- Embedding newline characters within the content field
- Including malicious BIND directives or additional DNS records after the newlines
- Submitting the record through the DomainZones::add() API endpoint
The injected content is written to the zone file and affects DNS resolution for the targeted domain.
The security patch addresses this vulnerability by adding proper validation for additional DNS record types:
} elseif ($type == 'LOC' && !empty($content)) {
if (!Validate::validateDnsLoc($content)) {
$errors[] = lng('error.dns_loc_invalid');
- } else {
- // keep content
- $content = $content;
}
} elseif ($type == 'MX') {
if ($prio === null || $prio < 0) {
Source: GitHub Commit Update
Detection Methods for CVE-2026-41230
Indicators of Compromise
- Unusual DNS record types (NAPTR, PTR, HINFO) in zone files that were not explicitly configured by administrators
- Zone files containing BIND directives ($INCLUDE, $ORIGIN, $GENERATE) that were not administratively configured
- DNS records with content containing unexpected newline characters or multi-line entries
- Audit log entries showing DNS record creation for uncommonly used record types
Detection Strategies
- Monitor Froxlor application logs for DNS zone modification requests using record types outside the standard set (A, AAAA, CNAME, MX, TXT, SRV, CAA)
- Implement file integrity monitoring on BIND zone files to detect unauthorized modifications
- Review DNS zone files periodically for unexpected directives or records that don't match the web interface configuration
- Deploy web application firewall rules to detect and block CRLF sequences in DNS record content fields
Monitoring Recommendations
- Enable detailed logging for all DNS zone modifications in Froxlor
- Set up alerts for zone file changes outside of scheduled maintenance windows
- Monitor for DNS resolution anomalies that could indicate zone file tampering
- Implement regular automated comparisons between database records and actual zone file contents
How to Mitigate CVE-2026-41230
Immediate Actions Required
- Upgrade Froxlor to version 2.3.6 or later immediately
- Audit existing DNS zone files for any suspicious records or injected content
- Review Froxlor audit logs for recent DNS zone modifications by customer accounts
- Validate all existing zone files against expected configuration
Patch Information
Froxlor has released version 2.3.6 which addresses this vulnerability. The patch adds proper validation for DNS record types and sanitizes content fields to prevent CRLF injection. The fix is available in commit 47a8af5d9523cb6ec94567405cfc2e294d3a1442.
Workarounds
- Restrict customer access to DNS zone management functionality until the patch is applied
- Implement input validation at the web server or WAF level to strip CRLF sequences from all input fields
- Manually audit and sanitize zone files after any customer-initiated modifications
- Consider temporarily disabling support for uncommonly used DNS record types at the application level
# Verify Froxlor version and check for suspicious zone entries
grep -E '(\$INCLUDE|\$ORIGIN|\$GENERATE)' /var/named/*.zone
# Review zone files for multi-line content that may indicate injection
awk '/^[^;]/ && NF > 4' /var/named/*.zone | head -50
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
