CVE-2021-21276

Privilege escalation in Polr

CRITICAL
9.3
CVSS Score
Published: February 1, 2021 at 12:00 AM UTC
Updated: June 17, 2026 at 03:35 AM UTC
2 products affected across 2 vendorsPolrPolr

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Severity
CRITICAL9.3
Exploit prediction
EPSS 7%

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 2.3.0
Affected range stops below 2.3.0, so it looks safe — our inference, not a vendor statement
v < 2.3.0
Affected range stops below 2.3.0, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

CVSS

9.3CRITICALGitHub_M
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality
HIGH
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-863NVD-CWE-Other

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