CVE-2026-103526 in Thelia
Summary
by MITRE • 10/12/2026
In Thelia v2.6.0, both the administrative login and forgotten password endpoints return different responses for invalid usernames and incorrect passwords, allowing unauthenticated attackers to enumerate valid administrator accounts. Because the endpoint also lacks rate limiting or other protections against repeated authentication attempts, username enumeration can be performed efficiently at scale.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability in Thelia version 2.6.0 represents a classic instance of user account enumeration stemming from inconsistent error handling within the application's authentication mechanisms. Specifically, both the administrative login endpoint and the forgotten password functionality exhibit distinct response behaviors when presented with invalid credentials versus valid usernames paired with incorrect passwords. This discrepancy allows an unauthenticated attacker to systematically probe the system by submitting various username inputs while using a dummy or known-invalid password. If the server returns a message indicating that the password is incorrect, it confirms that the specified username exists in the database. Conversely, if the response suggests that no account was found associated with that email address, the username can be ruled out as invalid. This side-channel information leakage effectively bypasses standard security controls by allowing attackers to build an accurate list of valid administrator accounts without needing prior knowledge or successful authentication credentials.
From a technical perspective, this flaw is rooted in poor input validation and error message sanitization practices during the development phase. The application fails to abstract the underlying database lookup results into generic responses that do not reveal specific failure points. Instead, it exposes internal state information through HTTP response bodies or status codes that differ based on whether the username exists but the password does not match, versus a completely non-existent user identity. This behavior is particularly dangerous in web applications because it transforms what should be an authentication barrier into a reconnaissance tool for adversaries seeking to target privileged accounts. The lack of rate limiting further exacerbates this issue by allowing automated scripts to iterate through thousands or millions of potential usernames rapidly without triggering account lockouts, CAPTCHAs, or IP-based throttling mechanisms that are standard defenses against brute-force and enumeration attacks.
The operational impact of this vulnerability is significant for organizations relying on Thelia as their e-commerce platform. By successfully enumerating valid administrator accounts, attackers can narrow the scope of subsequent attack vectors such as credential stuffing, dictionary attacks, or targeted phishing campaigns. Since administrative users often possess elevated privileges including access to customer data, financial records, and system configuration settings, compromising these accounts can lead to severe business disruption, regulatory non-compliance due to data breaches involving personally identifiable information, and direct financial loss through fraudulent transactions or ransomware deployment. The efficiency of the enumeration process means that even complex password policies may eventually be bypassed if attackers focus their efforts on a smaller set of confirmed valid targets rather than guessing randomly across all possible usernames.
This vulnerability aligns with CWE-204: Observable Response Discrepancy and CWE-287: Improper Authentication, as the application fails to treat authentication failures uniformly regardless of whether the username or password is incorrect. In terms of offensive security frameworks, this behavior facilitates reconnaissance activities categorized under MITRE ATT&CK technique T1087: Account Discovery, which attackers use to identify valid accounts before launching more destructive actions like privilege escalation or lateral movement within the network environment. The absence of rate limiting also relates to CWE-307: Improper Restriction of Excessive Authentication Attempts, highlighting a failure in implementing basic access control measures designed to mitigate automated abuse.
To remediate this vulnerability, developers must ensure that all authentication-related endpoints return identical error messages for both invalid usernames and incorrect passwords. A generic message such as "Invalid username or password" should be displayed regardless of which component of the credential pair is erroneous. Additionally, implementing robust rate limiting policies is critical to prevent automated enumeration at scale. This can include throttling requests per IP address, requiring CAPTCHA challenges after a small number of failed attempts, and enforcing account lockout mechanisms for administrative accounts after repeated failures. Security headers should also be configured to minimize information leakage in HTTP responses, ensuring that stack traces or detailed error logs are not exposed to end-users during production operations. Regular security testing including penetration tests focused on authentication flows can help identify similar discrepancies before they are exploited by malicious actors.