skip to content
Back to GitHub.com
Home Research Advisories CodeQL Wall of Fame Get Involved Events
October 20, 2021

GHSL-2021-116: ReDoS (Regular Expression Denial of Service) in pydal

Kevin Backhouse

Coordinated Disclosure Timeline

Summary

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

Product

pydal

Tested Version

v20200321.1

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.

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

reg = re.compile("[^']*('[^']*'[^']*)*\:(?P<clob>(C|B)LOB\('([^']+|'')*'\))")

# Doesn't terminate
reg.match("foo:CLOB('!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!)")

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-2021-116 in any communication regarding this issue.