#VU56458 Cross-site scripting in BookStack - CVE-2021-3767

Vulnerability identifier: #VU56458

Vulnerability risk: Low

CVSSv4.0: 0.9 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:P/U:Clear]

CVE-ID: CVE-2021-3767

CWE-ID: CWE-79

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
BookStack
Client/Desktop applications / Other client software

Vendor: Dan Brown

Description

The disclosed vulnerability allows a remote attacker to perform cross-site scripting (XSS) attacks.

The vulnerability exists due to insufficient sanitization of user-supplied data in app/Util/HtmlContentFilter.php. A remote authenticated attacker can trick the victim to follow a specially crafted link and execute arbitrary HTML and script code in user's browser in context of vulnerable website.

Successful exploitation of this vulnerability may allow a remote attacker to steal potentially sensitive information, change appearance of the web page, perform phishing and drive-by-download attacks.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

BookStack: 21.04 - 21.08.1

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External links
https://huntr.dev/bounties/7ec92c85-30eb-4071-8891-6183446ca980
https://github.com/bookstackapp/bookstack/commit/040997fdc4414776bcac06a3cbaac3b26b5e8a64

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote authenticated user via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, proof of concept for this vulnerability is available.