What is CVE-2021-3944?

CVE-2021-3944 is a medium-severity vulnerability in Bookstackapp Bookstack, classified under Cross-Site Request Forgery (CSRF). CVSS score: 6.8/10. Published 2021-12-02.

How severe is CVE-2021-3944?

Medium severity. CVSS v3 base score is 6.8 out of 10.

Is CVE-2021-3944 known to be exploited?

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

CSRF in Bookstackapp Bookstack

CVE-2021-3944

bookstack is vulnerable to Cross-Site Request Forgery (CSRF)

Vulnerability class: CSRF (Cross-Site Request Forgery)

Published 2021-12-02 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.8 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N.

EPSS exploit prediction

EPSS: 0.006 (48.7th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 49th percentile — 48.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: +0.000

Affected products

Bookstackapp Bookstack
Bookstackapp Bookstackapp/bookstack — versions unspecified

Weakness classification (CWE)

CWE-352 — Cross-Site Request Forgery (CSRF)

Public proof-of-concept exploits

References

huntr.dev/bounties/65551490-5ade-49aa-8b8d-274c2ca9fdc9 (Exploit, Patch, Third Party Advisory)
github.com/bookstackapp/bookstack/commit/88e6f93abf54192a69cc8080e0dc6516ee68cc… (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-3944?: CVE-2021-3944 is a medium-severity vulnerability in Bookstackapp Bookstack, classified under Cross-Site Request Forgery (CSRF). CVSS score: 6.8/10. Published 2021-12-02.
How severe is CVE-2021-3944?: Medium severity. CVSS v3 base score is 6.8 out of 10.
Is CVE-2021-3944 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.