CVE-2025-47781 is a critical vulnerability affecting Rallly, an open-source scheduling and collaboration tool, specifically versions up to and including 3.22.1. The vulnerability arises from the use of a weak token-based authentication mechanism where a 6-digit numeric code is sent to users via email to complete login. This token, due to its limited entropy (only 1 million possible combinations), is susceptible to brute force attacks. Compounding this weakness is the absence of any brute force protection or rate limiting on the authentication endpoint (/api/auth/callback/email). An attacker who knows a valid user's email address can attempt all possible 6-digit codes within the token's 15-minute validity window, making it feasible to compromise the account within that timeframe. Successful exploitation results in full account takeover, impacting confidentiality, integrity, and availability of user data and collaboration resources. The vulnerability is classified under CWE-331 (Insufficient Entropy) and carries a CVSS 3.1 score of 9.8 (critical), reflecting its ease of exploitation (network attack vector, no privileges or user interaction required) and severe impact. No patched versions are currently available, leaving all users of affected versions exposed. The recommended secure approach involves increasing token complexity to a high-entropy value that cannot be brute forced within the token lifetime and implementing rate limiting or lockout mechanisms on the authentication endpoint to prevent rapid repeated attempts.

For European organizations using Rallly for scheduling and collaboration, this vulnerability poses a significant risk. Account takeover can lead to unauthorized access to sensitive scheduling information, internal communications, and potentially linked systems if single sign-on or integrations are used. Confidentiality breaches could expose personal data protected under GDPR, leading to regulatory penalties and reputational damage. Integrity of scheduling data can be compromised, disrupting business operations and coordination. Availability may also be affected if attackers lock out legitimate users or manipulate schedules maliciously. Given the critical severity and ease of exploitation, attackers could target high-profile individuals or departments within organizations to gain footholds or conduct espionage. The lack of a patch means organizations must rely on compensating controls until a fix is released. The impact is heightened in sectors with strict compliance requirements or where scheduling data is sensitive, such as healthcare, government, and finance.

Immediate mitigation steps include implementing network-level protections such as Web Application Firewalls (WAFs) configured to detect and block rapid repeated requests to the /api/auth/callback/email endpoint, effectively rate limiting brute force attempts. Organizations should monitor authentication logs for unusual patterns indicative of brute force attacks. Where possible, temporarily disable or restrict access to Rallly instances until a patch is available. Encourage users to use unique email addresses not publicly exposed to reduce attacker knowledge of valid accounts. Consider deploying multi-factor authentication (MFA) mechanisms external to Rallly if integration is feasible, to add an additional layer of security. Developers and administrators should prioritize the release and deployment of patched versions that increase token entropy and implement server-side rate limiting. Additionally, educating users about phishing risks and suspicious login attempts can help detect exploitation attempts early.