What is CVE-2021-3874?

CVE-2021-3874 is a medium-severity vulnerability in Bookstackapp Bookstack, classified under Path Traversal. CVSS score: 6.5/10. Published 2021-10-15.

How severe is CVE-2021-3874?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Is CVE-2021-3874 known to be exploited?

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

Path Traversal in Bookstackapp Bookstack

CVE-2021-3874

bookstack is vulnerable to Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

Vulnerability class: Path Traversal (Directory Traversal)

Published 2021-10-15 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.012 (67.0th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 67th percentile — 67.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.012 · newest: 0.012 · change: 0.000

Affected products

Bookstackapp Bookstack
Bookstackapp Bookstackapp/bookstack — versions unspecified

Weakness classification (CWE)

CWE-22 — Path Traversal

Public proof-of-concept exploits

References

huntr.dev/bounties/ac268a17-72b5-446f-a09a-9945ef58607a (Exploit, Patch, Third Party Advisory)
github.com/bookstackapp/bookstack/commit/7224fbcc89f00f2b71644e36bb1b1d96addd1d… (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-3874?: CVE-2021-3874 is a medium-severity vulnerability in Bookstackapp Bookstack, classified under Path Traversal. CVSS score: 6.5/10. Published 2021-10-15.
How severe is CVE-2021-3874?: Medium severity. CVSS v3 base score is 6.5 out of 10.
Is CVE-2021-3874 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.