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December 8, 2021

GHSL-2021-115: ReDoS (Regular Expression Denial of Service) in Spyne

GitHub Security Lab

Coordinated Disclosure Timeline

Summary

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

Product

Spyne

Tested Version

spyne-2.13.16

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 Spyne 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

email_re = re.compile(
    r"[A-Za-z0-9!#-'\*\+\-/=\?\^_`\{-~]+"
    r"(\.[A-Za-z0-9!#-'\*\+\-/=\?\^_`\{-~]+)*@"
    # domain part is either a single symbol
    r"(([a-zA-Z0-9]|"
    # or have at least two symbols
    # hyphen can't be at the beginning or end of domain part
    # domain should contain at least 2 parts, the last one is TLD
    r"([a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])+)\.)+"
    # TLD should contain only letters, at least 2
    r"[A-Za-z]{2,}", re.IGNORECASE)

print(email_re.match("~.~@a0" + "0000" * 25))

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-2021-115 in any communication regarding this issue.