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December 8, 2021

GHSL-2021-121: ReDoS (Regular Expression Denial of Service) in StreamAlert

GitHub Security Lab

Coordinated Disclosure Timeline

Summary

StreamAlert contains a regular expression that is vulnerable to ReDoS (Regular Expression Denial of Service).

Product

StreamAlert

Tested Version

v3.4.1

Details

ReDoS

ReDoS, or Regular Expression Denial of Service, is a vulnerability affecting inefficient regular expressions which can perform extremely badly when run on a crafted input string.

This vulnerability was found using a CodeQL query which identifies inefficient regular expressions. You can see the results of the query on StreamAlert by following this link.

Vulnerability

The vulnerable regular expression is here.

To see that the regular expression is vulnerable, copy-paste it into a separate file as shown below:

import re

_URL_REGEX = re.compile(
    r'^(?:http(s)?://)?[\w.-]+(?:\.[\w\.-]+)+[\w\-\._~:/?#[\]@!\$&\'\(\)\*\+,;=.]+$'
)

_URL_REGEX.match("https://a.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-}");

Impact

This issue may lead to a denial of service.

Credit

This issue was discovered by GitHub team members @erik-krogh (Erik Krogh Kristensen) and @yoff (Rasmus Petersen).

Contact

You can contact the GHSL team at securitylab@github.com, please include a reference to GHSL-2021-121 in any communication regarding this issue.