MISP up to 2.5.39 JavaScript json_encode cross site scripting

Summaryinfo

A vulnerability was found in MISP up to 2.5.39 and classified as problematic. This impacts the function json_encode of the component JavaScript Handler. Such manipulation leads to cross site scripting. This vulnerability is listed as CVE-2026-54395. The attack may be performed from remote. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in MISP up to 2.5.39. It has been rated as problematic. Affected by this issue is the function json_encode of the component JavaScript Handler. The manipulation with an unknown input leads to a cross site scripting vulnerability. Using CWE to declare the problem leads to CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Impacted is integrity. CVE summarizes:

MISP contains a reflected cross-site scripting vulnerability in the UiBeta event index view. The urlparams value is inserted into an inline JavaScript handler using HTML escaping inside a single-quoted JavaScript string. Because browsers HTML-decode attribute values before JavaScript parsing, a crafted searcheventinfo value can restore encoded quote characters and break out of the JavaScript string. An attacker could craft a malicious URL that, when opened by a victim using the UiBeta event index, executes arbitrary JavaScript in the victim’s browser in the context of the MISP instance. The issue is fixed by encoding the value as a JavaScript string literal with json_encode() before applying HTML escaping at the attribute layer.

The weakness was presented by Jeroen Pinoy as b865deb036ca82dab272be260798f562034ba9ae. The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-54395 since 06/12/2026. The exploitation is known to be easy. The attack may be launched remotely. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1059.007.

Upgrading to version 2.5.40 eliminates this vulnerability. Applying the patch b865deb036ca82dab272be260798f562034ba9ae is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Name

• MISP

Version

• 2.5.0
• 2.5.1
• 2.5.2
• 2.5.3
• 2.5.4
• 2.5.5
• 2.5.6
• 2.5.7
• 2.5.8
• 2.5.9
• 2.5.10
• 2.5.11
• 2.5.12
• 2.5.13
• 2.5.14
• 2.5.15
• 2.5.16
• 2.5.17
• 2.5.18
• 2.5.19
• 2.5.20
• 2.5.21
• 2.5.22
• 2.5.23
• 2.5.24
• 2.5.25
• 2.5.26
• 2.5.27
• 2.5.28
• 2.5.29
• 2.5.30
• 2.5.31
• 2.5.32
• 2.5.33
• 2.5.34
• 2.5.35
• 2.5.36
• 2.5.37
• 2.5.38
• 2.5.39

License

• open-source

Website

• Product: https://github.com/MISP/MISP/

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