Skip to content

Catastrophic backtracking in URL authority parser when passed URL containing many @ characters

High severity GitHub Reviewed Published May 26, 2021 in urllib3/urllib3 • Updated Sep 2, 2023

Package

pip urllib3 (pip)

Affected versions

>= 1.25.4, < 1.26.5

Patched versions

1.26.5

Description

Impact

When provided with a URL containing many @ characters in the authority component the authority regular expression exhibits catastrophic backtracking causing a denial of service if a URL were passed as a parameter or redirected to via an HTTP redirect.

Patches

The issue has been fixed in urllib3 v1.26.5.

References

For more information

If you have any questions or comments about this advisory:

References

@sethmlarson sethmlarson published to urllib3/urllib3 May 26, 2021
Reviewed May 28, 2021
Published to the GitHub Advisory Database Jun 1, 2021
Published by the National Vulnerability Database Jun 29, 2021
Last updated Sep 2, 2023

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS score

0.292%
(70th percentile)

Weaknesses

CVE ID

CVE-2021-33503

GHSA ID

GHSA-q2q7-5pp4-w6pg

Source code

Credits

Loading Checking history
See something to contribute? Suggest improvements for this vulnerability.