CVE-2021-21276: Polr is an open source URL shortener

Q: How do I fix CVE-2021-21276?

polr: upgrade to 2.3.0. Exact commands for each OS are on this page.

Q: Is CVE-2021-21276 being exploited?

CVE-2021-21276 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-21276 affect?

CVE-2021-21276 affects polr. Severity is critical (CVSS 9.3). 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 reg

Q: How urgent is CVE-2021-21276?

Priority 66/100. Critical severity; EPSS top 6%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.3REMOTEUPGRADE

CVE-2021-21276 is a critical-severity flaw (CVSS 9.3) affecting polr. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 com

Why this priority

Critical severity
EPSS top 6%: very likely to be exploited
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.3 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	7.2% (top 6%)
CISA exploited list	No
Weakness	CWE-863
Published	2021-02-01
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: polrproject

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-02-01 15:15 UTCPublished CVE record published
2026-06-17 03:35 UTCUpdated Record last modified

polrproject polr UPGRADE

Affected: < 2.3.0

Fixed in: 2.3.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy polr || rpm -q polr || polr --version

2. UPGRADE to 2.3.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade polr

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade polr

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Exploit-DB: POLR URL 2.3.0 - Shortener Admin Takeover

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-21276?

polr: upgrade to 2.3.0. Exact commands for each OS are on this page.

Is CVE-2021-21276 being exploited?

CVE-2021-21276 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-21276 affect?

CVE-2021-21276 affects polr. Severity is critical (CVSS 9.3). 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 reg

How urgent is CVE-2021-21276?

Priority 66/100. Critical severity; EPSS top 6%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action

References

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