Stored XSS via malformed image extensions
Published Oct 27, 2021 · Updated Aug 3, 2024
Stored XSS in BookStack before 21.10.1 allows remote authenticated users with page-edit rights to upload browser-executable image content. ImageRepo::imageExtensionSupported() passes a single-quoted escape mask to trim(), so trailing letters such as the r in pngr are removed only during validation and the malformed extension is accepted. The attacker needs permission to create or update pages, and default local image storage publicly serves the uploaded content for execution in a visitor's browser.
Summary
What happened
Stored XSS in BookStack before 21.10.1 allows remote authenticated users with page-edit rights to upload browser-executable image content. ImageRepo::imageExtensionSupported() passes a single-quoted escape mask to trim(), so trailing letters such as the r in pngr are removed only during validation and the malformed extension is accepted. The attacker needs permission to create or update pages, and default local image storage publicly serves the uploaded content for execution in a visitor's browser.
The record
- CVE
- CVE-2021-3906
- Published
- Oct 27, 2021
- Updated
- Aug 3, 2024
- Vendor
- BookStack
- Product
- BookStack
- Classifications
- CWE-434, T1189
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Oct 27, 2021CVE publishedPublication date reported by the CVE source.
- Aug 3, 2024Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=unspecified <21.10.1
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Malformed pngr image upload proof of conceptproof of concept · unverified
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Technologies
Your stack
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Your stack
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