Arbitrary file upload in Bookstackapp Bookstack

CVE-2026-82450

BookStack before 26.05.4 contains a remote code execution vulnerability in the portable ZIP import functionality that allows users with Import Content and Create Books permissions to upload a PHP polyglot file as a book cover. Attackers can bypass image extension validation by embedding a PHP file with a .php filename in the ZIP archive, which is stored in the public web root and executed by unauthenticated requests.

Vulnerability class: Unrestricted File Upload

Published · last modified .

CVSS v3 metric

CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.010 (61.8th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 62nd percentile — 61.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-82450: held from 0.006 to 0.010.

EPSS over last 30 days · oldest: 0.006 · newest: 0.010 · change: +0.004

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-82450?
CVE-2026-82450 is a high-severity vulnerability in Bookstackapp Bookstack, classified under Unrestricted Upload of File with Dangerous Type. CVSS score: 8.8/10. Published 2026-08-29.
How severe is CVE-2026-82450?
High severity. CVSS v3 base score is 8.8 out of 10.