CVE-2026-121553 in Cotonti
Summary
by MITRE • 11/03/2026
Cotonti through 1.0.0 generates registration and email-change validation tokens with md5(microtime()), allowing attackers to bypass email-ownership verification by predicting tokens. Attackers can derive the generation time from the HTTP Date header and compute candidate tokens offline. They then submit these tokens to the users.register.php validate handler to activate accounts or confirm email addresses they do not control.
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Analysis
by VulDB Data Team • 11/03/2026
The vulnerability identified in Cotonti CMS versions through 1.0.0 stems from a critical flaw in the implementation of security-critical token generation mechanisms, specifically for user registration and email address change validation processes. The system relies on an MD5 hash constructed from the output of PHP's microtime function to create these tokens. This approach fundamentally violates established principles of cryptographic randomness because it utilizes a predictable source of entropy that is directly observable by external actors during normal web interactions. By leveraging this weak pseudo-random number generator, attackers can effectively bypass email ownership verification controls, which are designed to ensure that the individual controlling an account actually possesses access to the associated email address. This weakness allows malicious entities to create accounts or modify existing ones without legitimate authorization, undermining the integrity of user identity management within the application.
From a technical perspective, the core issue lies in the predictability of the input data used for hashing. The microtime function returns both the current Unix timestamp and microseconds since that timestamp. While this provides some variation, it is not cryptographically secure because an attacker can determine the approximate time window during which a token was generated by inspecting standard HTTP headers such as the Date header returned in server responses or observed via network traffic analysis. With knowledge of the generation algorithm and access to timing information from public-facing endpoints, attackers can perform offline brute-force attacks against the MD5 hash space within that narrow time frame. Since MD5 is also computationally fast and susceptible to collision attacks, this further reduces the effort required to find a valid token corresponding to a specific user or email address change request. The validation handler at users.register.php accepts these predicted tokens without additional verification steps, allowing unauthorized activation of accounts or confirmation of email addresses that do not belong to the requester.
The operational impact of this vulnerability is significant for any organization relying on Cotonti CMS for web applications requiring secure user registration and identity management. Attackers can register multiple fake accounts using valid-looking validation tokens derived from predictable timestamps, leading to account flooding, spam distribution, or reputation damage through malicious content posted under these fabricated identities. Furthermore, the ability to confirm email address changes without ownership verification enables privilege escalation scenarios where an attacker might take over existing user accounts by changing their associated email addresses to one they control. This compromises data confidentiality and integrity, as sensitive information linked to those accounts becomes accessible to unauthorized parties. In environments where multi-factor authentication or strict identity proofing is required for compliance with regulations such as GDPR or HIPAA, this flaw represents a severe non-compliance issue that could result in legal penalties and loss of customer trust.
This vulnerability aligns closely with CWE-330: Use of Insufficiently Random Values, which describes flaws where random values are generated using methods that do not provide adequate unpredictability for security purposes. Additionally, the exploitation technique relates to ATT&CK Tactic TA0001: Initial Access and specifically techniques involving account manipulation or credential stuffing if combined with other weaknesses. The lack of server-side entropy sources such as /dev/urandom on Unix-like systems or CryptGenRandom on Windows means the application fails to meet modern security standards for token generation. Mitigation strategies must prioritize replacing the current implementation with a cryptographically secure random number generator, such as PHP's random_int function or openssl_random_pseudo_bytes when available in older versions. Developers should also implement time-based rate limiting and challenge-response mechanisms that do not rely solely on server-generated tokens visible to clients. Regular security audits focusing on authentication flows and input validation logic are essential to prevent similar issues across the application ecosystem.