From: mame@... Date: 2021-05-21T18:00:01+00:00 Subject: [ruby-core:103953] [Ruby master Feature#17837] Add support for Regexp timeouts Issue #17837 has been updated by mame (Yusuke Endoh). We discussed this issue in today's dev-meeting. We agreed that, if we can find a good enough threshold, `Regexp#backtrack_limit=` is better than `Regexp#timeout=`. For example, * the threshold should stop almost all practical Regexps that run in about one minute, and * the threshold should NOT stop almost all practical Regexps that ends at most in a few seconds. Of course, it depends on the input and regexps, so we need to evaluate this in practical settings. We will wait for @sam.saffron's experiment. ---------------------------------------- Feature #17837: Add support for Regexp timeouts https://bugs.ruby-lang.org/issues/17837#change-92085 * Author: sam.saffron (Sam Saffron) * Status: Open * Priority: Normal ---------------------------------------- ### Background ReDoS are a very common security issue. At Discourse we have seen a few through the years. https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS In a nutshell there are 100s of ways this can happen in production apps, the key is for an attacker (or possibly innocent person) to supply either a problematic Regexp or a bad string to test it with. ``` /A(B|C+)+D/ =~ "A" + "C" * 100 + "X" ``` Having a problem Regexp somewhere in a large app is a universal constant, it will happen as long as you are using Regexps. Currently the only feasible way of supplying a consistent safeguard is by using `Thread.raise` and managing all execution. This kind of pattern requires usage of a third party implementation. There are possibly issues with jRuby and Truffle when taking approaches like this. ### Prior art .NET provides a `MatchTimeout` property per: https://docs.microsoft.com/en-us/dotnet/api/system.text.regularexpressions.regex.matchtimeout?view=net-5.0 Java has nothing built in as far as I can tell: https://stackoverflow.com/questions/910740/cancelling-a-long-running-regex-match Node has nothing built in as far as I can tell: https://stackoverflow.com/questions/38859506/cancel-regex-match-if-timeout Golang and Rust uses RE2 which is not vulnerable to DoS by limiting features (available in Ruby RE2 gem) ``` irb(main):003:0> r = RE2::Regexp.new('A(B|C+)+D') => # irb(main):004:0> r.match("A" + "C" * 100 + "X") => nil ``` ### Proposal Implement `Regexp.timeout` which allow us to specify a global timeout for all Regexp operations in Ruby. Per Regexp would require massive application changes, almost all web apps would do just fine with a 1 second Regexp timeout. If `timeout` is set to `nil` everything would work as it does today, when set to second a "monitor" thread would track running regexps and time them out according to the global value. ### Alternatives I recommend against a "per Regexp" API as this decision is at the application level. You want to apply it to all regular expressions in all the gems you are consuming. I recommend against a move to RE2 at the moment as way too much would break ### See also: https://people.cs.vt.edu/davisjam/downloads/publications/Davis-Dissertation-2020.pdf https://levelup.gitconnected.com/the-regular-expression-denial-of-service-redos-cheat-sheet-a78d0ed7d865 -- https://bugs.ruby-lang.org/ Unsubscribe: