Description

Rybbit before 2.7.0 contains a CORS misconfiguration vulnerability that allows attackers to bypass origin restrictions by reflecting any request origin in Access-Control-Allow-Origin responses while credentials are enabled. Attackers can issue credentialed cross-origin requests from any website to read analytics data, account information, and perform authenticated state-changing operations as the victim user.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.1",
  "pubDate": "2026-08-28T20:20:20.243Z",
  "pubdate": "2026-08-28T20:20:20.243Z",
  "executiveSummary": "Rybbit versions prior to 2.7.0 are affected by a critical Cross-Origin Resource Sharing (CORS) misconfiguration. The vulnerability stems from an insecure implementation that dynamically reflects the 'Origin' request header into the 'Access-Control-Allow-Origin' response header while concurrently enabling 'Access-Control-Allow-Credentials'.\nThis flaw effectively nullifies the Same-Origin Policy (SOP) protections intended to prevent unauthorized cross-origin data access. An attacker can orchestrate a malicious web page to execute authenticated, cross-origin HTTP requests against the Rybbit application on behalf of an unsuspecting, authenticated user. The impact is significant, allowing unauthorized third parties to extract sensitive analytics data, retrieve account-specific information, and execute state-changing operations within the application.\nThe vulnerability requires no prior authentication from the attacker's perspective, relying instead on the victim's existing session state. Because the application blindly trusts the 'Origin' header provided by the client, it fails to enforce strict allow-listing, thereby exposing all authenticated users to potential session hijacking and data exfiltration. Given the ability to perform authenticated actions, the risk level is high, necessitating immediate upgrades to version 2.7.0 or higher to restore security boundaries.",
  "technicalDetails": "The vulnerability resides within the Rybbit application's CORS middleware or request handling logic, specifically in the configuration of cross-origin security headers. The root cause is an insecure dynamic reflection pattern where the server-side code parses the 'Origin' header from incoming HTTP requests and reflects the exact value into the 'Access-Control-Allow-Origin' header without validation against a predefined, trusted whitelist.\nThis implementation flaw is exacerbated by the inclusion of the 'Access-Control-Allow-Credentials: true' header. Under the standard CORS specification, when credentials (such as cookies or Authorization headers) are allowed, the browser mandates that the server must explicitly define the permitted origin rather than utilizing a wildcard or simple reflection. By reflecting the attacker-controlled origin, the application instructs the victim's browser to bypass security constraints, granting the malicious site full access to the response body of requests made to the Rybbit instance.\nThe attack flow is executed as follows: 1) An attacker hosts a malicious website designed to trigger background fetch or XHR requests to the target Rybbit API. 2) The attacker lures an authenticated Rybbit user to the malicious domain. 3) The browser initiates a cross-origin request to Rybbit; since the user is authenticated, the browser automatically attaches the victim's session cookies. 4) The Rybbit server processes the request, reads the attacker's domain from the 'Origin' header, and reflects it in the 'Access-Control-Allow-Origin' response header. 5) The browser detects a matching origin policy and allows the malicious script to read the sensitive response data or perform actions on the API.\nBecause the server blindly trusts the origin header, the attacker does not require specific privileges; they only require the victim to have an active, authenticated session with the Rybbit application. The impact of this exploit is comprehensive, encompassing the exfiltration of personally identifiable information (PII), theft of session-dependent data, and the unauthorized execution of administrative or user-level state-changing operations via forged requests. This vulnerability effectively bypasses the browser's security sandbox, turning the victim's own browser into a conduit for unauthorized data exfiltration and persistent cross-site request forgery (CSRF)-like attacks."
}