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Fix CVE-2017-16100: Abandon validation using an unsafe regex pattern in favor of tokenizing and applying a linear pattern #10

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Fix CVE-2017-16100: Abandon validation using an unsafe regex pattern in favor of tokenizing and applying a linear pattern #10

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20 changes: 16 additions & 4 deletions lib/dns-sync.js
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Original file line number Diff line number Diff line change
Expand Up @@ -5,9 +5,6 @@ var util = require('util'),
shell = require('shelljs'),
debug = require('debug')('dns-sync');

//source - http://stackoverflow.com/questions/106179/regular-expression-to-match-dns-hostname-or-ip-address
var ValidHostnameRegex = new RegExp("^(([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9])$");

// https://nodejs.org/api/dns.html#dns_dns_resolve_hostname_rrtype_callback
var RRecordTypes = [
'A',
Expand All @@ -22,8 +19,23 @@ var RRecordTypes = [
'TXT',
'ANY'];

/* RFC 1123: https://datatracker.ietf.org/doc/html/rfc1123
* For a hostname to be valid:
* 1. It needs to have less than 254 chars (255 - 1 for the omitted delimiter of root label)
* 2. Each label should have less than 64 chars but less 63 for right-most label
* 3. Labels are delimited by a period
* 4. Labels start and end with alphanumeric but can have - in middle
*/
const validLabelPattern = /^[a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?$/;
function isValidHostName(hostname) {
return ValidHostnameRegex.test(hostname);
if (typeof hostname !== 'string') return false;

let cleanHostname = hostname.endsWith('.') ? hostname.slice(0, -1) : hostname;
if (cleanHostname.length >= 254) return false;

return cleanHostname
.split('.')
.every(label => validLabelPattern.test(label));
}
/**
* Resolve hostname to IP address,
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5 changes: 5 additions & 0 deletions test/test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,8 @@ describe('dns sync', function () {
assert.ok(dnsSync.resolve('www.paypal.com'));
assert.ok(dnsSync.resolve('www.google.com'));
assert.ok(dnsSync.resolve('www.yahoo.com'));
assert.ok(dnsSync.resolve('0'.repeat(63) + '.000'));
assert.ok(dnsSync.resolve('0'.repeat(63) + '.' + '0'.repeat(63)));
});

it('should fail to resolve dns', function () {
Expand All @@ -24,6 +26,9 @@ describe('dns sync', function () {
assert.ok(!dnsSync.resolve("$(id > /tmp/foo)'"));
assert.ok(!dnsSync.resolve("cd /tmp; rm -f /tmp/echo; env 'x=() { (a)=>' bash -c \"echo date\"; cat /tmp/echo"));
assert.ok(!dnsSync.resolve("$(grep -l -z '[^)]=() {' /proc/[1-9]*/environ | cut -d/ -f3)'"));
assert.ok(!dnsSync.resolve('0-' + '00000'.repeat(29) + '\\n'));
assert.ok(!dnsSync.resolve('0'.repeat(64) + '.000'));
assert.ok(!dnsSync.resolve('0.' + '0'.repeat(64)));
});

it('should resolve AAAA records if asked', function () {
Expand Down