High severity · published Aug 29, 2026
CVE-2026-82450
BookStack before 26.05.4 Remote Code Execution via Book Cover
8.8
CVSS
1%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)1.0% · higher than 63% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
BO
bookstack · bookstackapp
before 26.05.4 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-82450
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-82450
patch
https://github.com/BookStackApp/BookStack/commit/e210cc32e4cbb1efeae5c5c9d0fef8e3c6a752e6
product
https://github.com/BookStackApp/BookStack
third-party-advisory
https://www.vulncheck.com/advisories/bookstack-before-26.05.4-remote-code-execution-via-book-cover
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