What is CVE-2021-34254?

CVE-2021-34254 is a medium-severity vulnerability in Umbraco Cms, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 6.1/10. Published 2021-06-28.

How severe is CVE-2021-34254?

Medium severity. CVSS v3 base score is 6.1 out of 10.

Is CVE-2021-34254 known to be exploited?

3 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Open Redirect in Umbraco Cms

CVE-2021-34254

Umbraco CMS before 7.15.7 is vulnerable to Open Redirection due to insufficient url sanitization on booting.aspx.

Vulnerability class: Open Redirect

Published 2021-06-28 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.007 (51.7th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 52nd percentile — 51.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.007 · newest: 0.007 · change: 0.000

Affected products

Umbraco Cms

Weakness classification (CWE)

CWE-601 — URL Redirection to Untrusted Site (Open Redirect)

Public proof-of-concept exploits

References

github.com/umbraco/Umbraco-CMS/issues/9782 (Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2021-34254?: CVE-2021-34254 is a medium-severity vulnerability in Umbraco Cms, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 6.1/10. Published 2021-06-28.
How severe is CVE-2021-34254?: Medium severity. CVSS v3 base score is 6.1 out of 10.
Is CVE-2021-34254 known to be exploited?: 3 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.