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dns: setServers has super-linear regex #20443
Description
- Version
./out/Release/node --version
v11.0.0-pre
- Platform
(20:24:36) jamie@woody ~/Desktop/floss/node $ uname -a
Linux woody 4.13.0-38-generic #43~16.04.1-Ubuntu SMP Wed Mar 14 17:48:43 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
- Subsystem
DNS
Problematic behavior
I recently scanned lib/ with my vuln-regex-detector tools and found a super-linear regex in lib/dns.js.
Here is a demo:
(20:20:05) jamie@woody ~ $ cat /tmp/node-dns-poc.js
#!/usr/bin/env node
const dns = require('dns');
const badServer = '['.repeat(100000);
console.log('Setting badServer');
try {
dns.setServers([badServer]);
} catch (e) {}
console.log('Done');
(20:20:06) jamie@woody ~ $ time /tmp/node-dns-poc.js
Setting badServer
Done
real 0m6.330s <------- Ouch.
user 0m6.326s
sys 0m0.004s
The long execution time is due to this unsafe regex:
Resolver.prototype.setServers = setServers;
function setServers(servers) {
// cache the original servers because in the event of an error setting the
// servers cares won't have any servers available for resolution
const orig = this._handle.getServers();
const newSet = [];
const IPv6RE = /\[(.*)\]/; <---------- Quadratic complexityI submitted this via HackerOne for assessment and it was deemed not a likely threat vector. I agree with this assessment, since I really hope most users aren't letting clients set their DNS servers.
However, this is still a potential performance bug. I am working on a PR.
Activity
dns: revise quadratic regex in setServers
dns: improve setServers() errors and performance
dns: improve setServers() errors and performance
dns: improve setServers() errors and performance