This issue was successfully tested on Link Library version 126.96.36.199.
This issue is fixed in version 188.8.131.52
Cross-Site Scripting (XSS) attacks are a type of injection, in which malicious scripts are injected into otherwise benign and trusted web sites. XSS attacks occur when an attacker uses a web application to send malicious code, generally in the form of a browser side script, to a different end user. Flaws that allow these attacks to succeed are quite widespread and occur anywhere a web application uses input from a user within the output it generates without validating or encoding it. Reflected XSS occurs when user input is immediately returned by a web application in an error message, search result, or any other response that includes some or all of the input provided by the user as part of the request
sucessupdatecount fields do not validate
<script> tags and do not perform output encoding.
885: echo echo "<div id='message' class='updated fade'><p><strong>" . ($_GET['successimportcount'] : '0') . " " . __('link(s) imported', 'link-library') . ", " . ($_GET['successupdatecount'] : '0') . " " . __('link(s) updated', 'link-library') . ".</strong></p></div>";
Proof of concept