Description

Unauthenticated Cross Site Scripting (XSS) in Simply Schedule Appointments <= 1.6.12.10 versions.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.1",
  "pubDate": "2026-08-06T15:17:15.233Z",
  "pubdate": "2026-08-06T15:17:15.233Z",
  "executiveSummary": "An unauthenticated Cross-Site Scripting (XSS) vulnerability has been identified in the Simply Schedule Appointments plugin, affecting versions 1.6.12.10 and prior. This security flaw enables remote, unauthenticated threat actors to inject malicious client-side scripts, typically JavaScript, into victim browsers via vulnerable application parameters.\nThe primary impact of this vulnerability involves the execution of arbitrary script code in the context of a targeted user's browser session. Depending on the privileges of the victim interacting with the compromised application interface, successful exploitation can lead to session hijacking, credential theft, sensitive data exposure, and unauthorized actions performed on behalf of the user.\nThe vulnerability resides within the input handling and output rendering mechanisms of the Simply Schedule Appointments product. Because the flaw does not require authentication, any remote network-adjacent or external attacker can initiate exploitation attempts without possessing pre-existing user credentials or administrative privileges.\nOrganizations utilizing the affected software versions face significant risk regarding client-side integrity and user trust. Immediate remediation is strongly advised through software updates to eliminate the underlying input validation and output encoding deficiencies.",
  "technicalDetails": "The vulnerability is an unauthenticated Cross-Site Scripting (XSS) flaw present in Simply Schedule Appointments version 1.6.12.10 and earlier. The root cause stems from insufficient input sanitization and a lack of proper context-aware output encoding on user-supplied parameters processed by the plugin.\nNetwork exposure is external, as the vulnerable application components are accessible over standard web protocols (HTTP/HTTPS) without requiring any authentication credentials or session state. Consequently, unauthenticated attackers can craft malicious requests containing payload strings destined for reflection or storage within the web application interface.\nThe attack flow proceeds as follows: First, the threat actor crafts a malicious URL or payload containing executable JavaScript encapsulated within HTML tags or event handlers designed for injection into the vulnerable input vector of Simply Schedule Appointments. Second, the attacker induces an unauthenticated victim to access the malicious link or interact with the compromised endpoint. Third, the application processes the untrusted input and reflects or renders it back within the Document Object Model (DOM) of the victim's browser without adequate escaping. Finally, the victim's browser parses the malicious payload as legitimate markup, executing the arbitrary script in the security context of the victim's session.\nThe vulnerable component involves specific input processing functions and rendering templates within the Simply Schedule Appointments plugin that fail to enforce strict input validation policies. The payload behavior typically involves executing arbitrary JavaScript to manipulate the DOM, exfiltrate session cookies, perform unauthorized API requests, or redirect users to malicious landing pages.\nPost-exploitation impact is constrained by the privileges of the user viewing the affected page, but can range from localized defacement to comprehensive account compromise if administrative interfaces or sessions are targeted. The absence of authentication requirements significantly lowers the barrier to entry for potential attackers aiming to automate exploitation against target installations."
}