What is CVE-2021-4000?

CVE-2021-4000 is a medium-severity vulnerability in Showdoc, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 6.1/10. Published 2021-12-03.

How severe is CVE-2021-4000?

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

Is CVE-2021-4000 known to be exploited?

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

Open Redirect in Showdoc

CVE-2021-4000

showdoc is vulnerable to URL Redirection to Untrusted Site

Vulnerability class: Open Redirect

Published 2021-12-03 · 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: 0.008 (56.5th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 56th percentile — 56.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: +0.000

Affected products

Showdoc
Star7th Star7th/showdoc — versions unspecified

Weakness classification (CWE)

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

Public proof-of-concept exploits

References

huntr.dev/bounties/e4d803e0-3104-432c-80b3-34bc453c8962 (Exploit, Third Party Advisory)
github.com/star7th/showdoc/commit/c7f10033eba5f2b5a537f9af9ba2379138e67138 (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-4000?: CVE-2021-4000 is a medium-severity vulnerability in Showdoc, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 6.1/10. Published 2021-12-03.
How severe is CVE-2021-4000?: Medium severity. CVSS v3 base score is 6.1 out of 10.
Is CVE-2021-4000 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.