CVE-2026-100678 in stoatchat
Summary
by MITRE • 09/26/2026
stoatchat before 0.15.5 fails to enforce account-level attempt limits on MFA login challenges, allowing attackers who know a password to guess TOTP codes with only IP-based rate limiting. Attackers can reuse MFA challenge tickets across multiple failed attempts and distribute guesses across IP addresses to bypass rate limiting and gain account access.
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Analysis
by VulDB Data Team • 09/26/2026
The vulnerability in stoatchat versions prior to 0.15.5 represents a critical failure in the implementation of Multi-Factor Authentication (MFA) security controls, specifically regarding how authentication challenges are managed during the login process. The core technical flaw lies in the application's inability to enforce account-level attempt limits for Time-based One-Time Password (TOTP) verification. Instead of tracking and limiting failed MFA attempts on a per-user basis, the system relies exclusively on IP-based rate limiting mechanisms. This architectural decision creates a significant security gap because it decouples the authentication state from the specific user identity during the challenge phase, allowing attackers to circumvent standard brute-force protections that are designed to lock out accounts after repeated failures.
From an operational perspective, this flaw allows an attacker who has already obtained or guessed a valid password for a target account to bypass the MFA layer through systematic guessing of TOTP codes. Since TOTP codes are typically six-digit numeric values generated by authenticator apps, there is a finite and relatively small search space of one million possible combinations per time step. Without account-level throttling, an attacker can attempt all or a significant portion of these combinations without triggering any lockout mechanisms associated with the specific user identity. The reliance on IP-based rate limiting further exacerbates this risk by enabling distributed attack strategies. Attackers can distribute their guessing attempts across multiple source IP addresses using proxy networks or botnets to stay below the threshold that would trigger an IP block, effectively rendering the rate-limiting control useless against determined adversaries with sufficient resources.
The ability to reuse MFA challenge tickets is a critical component of this vulnerability's exploitability. In many secure implementations, each authentication attempt generates a new unique token or invalidates previous ones to prevent replay attacks and limit the window for guessing. However, in stoatchat versions affected by this issue, attackers can retain access to a single valid MFA challenge ticket across multiple failed attempts. This persistence allows them to continuously submit guesses against the same cryptographic seed without needing to re-authenticate with the password or request new time-based codes repeatedly, thereby streamlining the brute-force process and increasing the probability of success within a short timeframe.
This vulnerability aligns closely with CWE-307 Improper Restriction of Excessive Authentication Attempts, as it fails to limit the number of authentication attempts for a single account. Furthermore, from an adversary tactics perspective, this flaw facilitates Credential Stuffing and Brute Force attacks under MITRE ATT&CK technique T1110. The ability to bypass MFA protections through distributed guessing undermines one of the most effective layers of defense against unauthorized access, potentially leading to full account compromise, data exfiltration, or lateral movement within an organization if the compromised account has elevated privileges.
To mitigate this vulnerability, it is imperative for developers and system administrators to implement strict account-level rate limiting that tracks failed MFA attempts independently of the source IP address. The authentication logic should enforce a maximum number of allowed TOTP guesses per time window before temporarily locking the specific user's ability to authenticate or requiring additional verification steps such as CAPTCHA challenges or administrative intervention. Additionally, implementing challenge ticket expiration and invalidation after each attempt would prevent the reuse of tokens across multiple guessing iterations. Upgrading to stoatchat version 0.15.5 or later is required to resolve these issues, as newer versions are expected to enforce proper account-level constraints on MFA login challenges. Organizations should also consider implementing adaptive authentication strategies that monitor for anomalous behavior patterns indicative of distributed brute-force attacks and respond with dynamic security controls such as temporary suspensions or enhanced verification requirements.