What is CVE-2021-3915?

CVE-2021-3915 is a medium-severity vulnerability in Bookstackapp Bookstack, classified under Unrestricted Upload of File with Dangerous Type. CVSS score: 5.7/10. Published 2021-11-13.

How severe is CVE-2021-3915?

Medium severity. CVSS v3 base score is 5.7 out of 10.

Arbitrary file upload in Bookstackapp Bookstack

CVE-2021-3915

bookstack is vulnerable to Unrestricted Upload of File with Dangerous Type

Vulnerability class: Unrestricted File Upload

Published 2021-11-13 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.7 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.010 (60.1th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 60th percentile — 60.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.009 · newest: 0.010 · change: +0.000

Affected products

Bookstackapp Bookstack
Bookstackapp Bookstackapp/bookstack — versions unspecified

Weakness classification (CWE)

CWE-434 — Unrestricted Upload of File with Dangerous Type

References

huntr.dev/bounties/fcb65f2d-257a-46f4-bac9-f6ded5649079 (Exploit, Patch, Third Party Advisory)
github.com/bookstackapp/bookstack/commit/ae155d67454d6b9f6c93b2bb457aaa4b2eb1a9… (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-3915?: CVE-2021-3915 is a medium-severity vulnerability in Bookstackapp Bookstack, classified under Unrestricted Upload of File with Dangerous Type. CVSS score: 5.7/10. Published 2021-11-13.
How severe is CVE-2021-3915?: Medium severity. CVSS v3 base score is 5.7 out of 10.