CVE-2026-56312 in Capgo
Summary
by MITRE • 07/10/2026
Capgo before 12.128.2 contains an improper validation vulnerability in the accept_invitation endpoint that creates user accounts before captcha validation is enforced. Attackers can bypass captcha protection by sending POST requests with invalid captcha tokens to create unwanted accounts and burn invite links.
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Analysis
by VulDB Data Team • 07/10/2026
The vulnerability in Capgo versions prior to 12.128.2 represents a critical improper input validation flaw that directly undermines the application's account creation security controls. This weakness exists within the accept_invitation endpoint where the system fails to properly validate captcha tokens before proceeding with user account creation. The flaw allows malicious actors to bypass the intended security measures by sending crafted POST requests containing invalid or nonexistent captcha tokens while still successfully creating user accounts. This represents a fundamental breakdown in the application's defense-in-depth strategy and violates core security principles outlined in CWE-20, which addresses improper input validation as one of the most prevalent software vulnerabilities.
The operational impact of this vulnerability extends beyond simple account creation abuse to encompass significant resource depletion and potential service disruption. Attackers can systematically consume available invite links by creating accounts with invalid captcha tokens, effectively burning through legitimate invitation resources and potentially blocking genuine users from accessing the service. This type of abuse directly impacts the application's availability and can lead to denial-of-service conditions for legitimate users who require valid invitations to access restricted functionality. The vulnerability creates an attack surface that aligns with ATT&CK technique T1078.004, which covers bypassing account lockout mechanisms through automated account creation, and demonstrates how weak validation controls can be exploited to perform unauthorized account provisioning.
The technical implementation flaw stems from improper order of operations within the endpoint logic where account creation occurs before captcha validation is enforced, creating a race condition that allows privilege escalation through account manipulation. This design error violates security best practices by not implementing proper state validation and authentication checks before executing account creation operations. The vulnerability can be exploited using automated tools or scripts that rapidly send POST requests to the endpoint with malformed captcha data, enabling mass account generation without legitimate verification. Security controls that should have been in place include mandatory captcha validation prior to any account creation process, input sanitization of all request parameters, and proper error handling that prevents account creation when validation fails.
Mitigation strategies should focus on implementing immediate patching of the vulnerable endpoint to enforce captcha validation before any account creation occurs, with additional layers of security including rate limiting to prevent automated exploitation. The system should be configured to reject requests containing invalid or expired captcha tokens immediately without proceeding to account creation steps, while also implementing proper logging and monitoring for suspicious account creation patterns that could indicate abuse attempts. Organizations should consider implementing CAPTCHA token validation timeouts, request throttling mechanisms, and additional authentication factors such as email verification or phone number confirmation to create multiple barriers against automated account creation abuse. The fix should align with CWE-1321 guidelines for proper validation of inputs before processing and implement proper separation of concerns between validation and execution phases within the application logic, ensuring that all security controls are enforced in the correct sequence to prevent unauthorized access and resource consumption.