Internet Bug Bounty: curl cookie mixed case PSL bypass

2023-12-0612:00:29

nyymi

hackerone.com

$2540

curl

super cookies

vulnerability

public suffix list

bypass

6.5 Medium

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

LOW

Integrity Impact

LOW

Availability Impact

NONE

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

6.7 Medium

AI Score

Confidence

High

6.4 Medium

CVSS2

Access Vector

NETWORK

Access Complexity

LOW

Authentication

NONE

Confidentiality Impact

PARTIAL

Integrity Impact

PARTIAL

Availability Impact

NONE

AV:N/AC:L/Au:N/C:P/I:P/A:N

0.001 Low

EPSS

Percentile

28.7%

JSON

A vulnerability in curl allows a malicious HTTP server to set “super cookies” in curl that are then passed back to more origins than what is otherwise allowed or possible. This allows a site to set cookies that then would get sent to different and unrelated sites and domains.

It could do this by exploiting a mixed case flaw in curl’s function that verifies a given cookie domain against the Public Suffix List (PSL). For example a cookie could be set with domain=co.UK when the URL used a lowercase hostname curl.co.uk, even though co.uk is listed as a PSL domain.