jarun Buku up to 5.1.1 /api/fetch_data is_bad_url server-side request forgery

Summaryinfo

A vulnerability categorized as critical has been discovered in jarun Buku up to 5.1.1. This issue affects the function is_bad_url of the file /api/fetch_data. Such manipulation of the argument url leads to server-side request forgery. This vulnerability is referenced as CVE-2026-123201. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability was found in jarun Buku up to 5.1.1 and classified as critical. Affected by this issue is the function is_bad_url of the file /api/fetch_data. The manipulation of the argument url with an unknown input leads to a server-side request forgery vulnerability. Using CWE to declare the problem leads to CWE-918. The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. Impacted is confidentiality, integrity, and availability. CVE summarizes:

Buku (bukuserver) through 5.1.1 contains an unauthenticated server-side request forgery vulnerability that allows remote attackers to make the server request internal hosts by supplying a url parameter to /api/fetch_data or /api/network_handle. Attackers can target loopback, private, or cloud metadata IP addresses, which pass the weak is_bad_url() check and follow redirects, to discover internal services and read their page titles, descriptions, and keywords.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-123201 since 11/05/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 11/05/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Vendor

• jarun

Name

• Buku

Version

• 5.1.0
• 5.1.1

Website

• Product: https://github.com/jarun/buku/

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