CVE-2026-126811: Auth Bypass (CVSS 5.4)

Description

BookStack before 26.09.3 contains an incorrect authorization vulnerability that allows authenticated users to access other users' unpublished draft page images by checking only PageView permission without draft status. Attackers can read drawio data via the base64 endpoint or rename, replace, or delete draft images by sequential ID to disclose or tamper with unpublished work.

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CVSS v3.1 Score

5.4

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

EPSS — Exploit Prediction

0.0029

Probability of exploitation

0.22%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-863 Incorrect Authorization

References

Other References

https://codeberg.org/bookstack/bookstack/commit/4fec06236cbfb314fd72c1b3614c7c50162fb41c https://codeberg.org/bookstack/bookstack/commit/926e16a23f346be47d44746d14cba40cb355cbe1 https://codeberg.org/bookstack/bookstack/releases/tag/v26.09.3 https://github.com/BookStackApp/BookStack/blob/v26.09.2/app/Uploads/Controllers/DrawioImageController.php#L82-L92 https://github.com/BookStackApp/BookStack/blob/v26.09.2/app/Uploads/Controllers/ImageController.php#L159-L169 https://github.com/BookStackApp/BookStack/commit/926e16a23f346be47d44746d14cba40cb355cbe1 https://github.com/BookStackApp/BookStack/releases/tag/v26.09.3 https://github.com/fishtankyu/bookstack-draft-image-idor-advisory.md https://www.bookstackapp.com/blog/bookstack-release-v26-09-3/ https://www.vulncheck.com/advisories/bookstack-before-26.09.3-incorrect-authorization-via-image-and-drawio-endpoints

Frequently Asked Questions

What is CVE-2026-126811? +

BookStack before 26.09.3 contains an incorrect authorization vulnerability that allows authenticated users to access other users' unpublished draft page images by checking only PageView permission without draft status. Attackers can read drawio data via the base64 endpoint or rename, replace, or delete draft images by sequential ID to disclose or tamper with unpublished work. It has a CVSS v3.1 base score of 5.4 (MEDIUM).

How severe is CVE-2026-126811? +

CVE-2026-126811 has a CVSS v3.1 score of 5.4 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0029, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-126811? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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