$ cve CVE-2021-21276 JSON

CVE-2021-21276 EXPLOIT

9.3

CRITICAL · CVSS 3.1 · EPSS 7.2% (pctl 94)

Patch early

A public exploit exists.

Description

Polr is an open source URL shortener. in Polr before version 2.3.0, a vulnerability in the setup process allows attackers to gain admin access to site instances, even if they do not possess an existing account. This vulnerability exists regardless of users' settings. If an attacker crafts a request with specific cookie headers to the /setup/finish endpoint, they may be able to obtain admin privileges on the instance. This is caused by a loose comparison (==) in SetupController that is susceptible to attack. The project has been patched to ensure that a strict comparison (===) is used to verify the setup key, and that /setup/finish verifies that no users table exists before performing any migrations or provisioning any new accounts. This is fixed in version 2.3.0. Users can patch this vulnerability without upgrading by adding abort(404) to the very first line of finishSetup in SetupController.php.

Scoring

CVSS	9.3 (CRITICAL, v3.1)
Vector	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N
EPSS	7.16% — more likely to be exploited than 94% of all CVEs
Weakness	CWE-863
On CISA KEV	no
Public exploit	yes
Published	2021-02-01
Last modified	2026-06-17

Affected (1)

Vendor	Product
polrproject	polr

Public exploits

Source	Title	Date
exploit-db	POLR URL 2.3.0 - Shortener Admin Takeover	2023-04-06

References

→ the Explorer · watch your stack · NVD