CVE-2026-97736 in tinyauth
Summary
by MITRE • 09/25/2026
tinyauth before 5.1.3 allows rule bypass by appending an allowed route string. This is caused by an unanchored regular expression.
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Analysis
by VulDB Data Team • 09/25/2026
The vulnerability identified in tinyauth versions prior to 5.1.3 represents a critical security flaw rooted in improper input validation and the misuse of regular expressions for access control logic. Specifically, the authentication middleware relies on an unanchored regular expression to match incoming request routes against a predefined list of allowed paths. In regex syntax, an unanchored pattern matches if the specified sequence appears anywhere within the target string, rather than requiring it to constitute the entire path from start to finish. This design oversight allows attackers to craft malicious URLs that contain valid route segments as substrings but append additional characters or parameters after them. For instance, if a rule permits access to /admin/dashboard, an attacker could potentially bypass this restriction by requesting /admin/dashboard/evil_payload, provided the regex does not enforce end-of-string anchoring. This technique effectively circumvents the intended authorization checks because the validation logic confirms that the allowed route exists within the URL but fails to verify that no unauthorized extensions or sub-paths are present.
From a technical perspective, this flaw is classified under CWE-20: Improper Input Validation and more specifically aligns with CWE-184: Incomplete List of Validated Inputs. The root cause lies in the failure to anchor the regular expression using start-of-string (^) and end-of-string ($) anchors or equivalent strict matching mechanisms. Without these constraints, the validation logic is inherently permissive beyond its intended scope. This type of vulnerability is particularly dangerous because it often goes undetected during standard testing unless specific fuzzing techniques are employed to test for substring matches against allowed lists. The lack of strict boundary checking means that any subsequent path components or query parameters appended after a valid route segment are treated as part of the authenticated context, potentially granting access to restricted resources or functionality that should remain isolated from unauthenticated users.
The operational impact of this vulnerability can be severe depending on the application's architecture and the sensitivity of the bypassed routes. If an attacker successfully exploits this rule bypass, they may gain unauthorized access to administrative interfaces, sensitive data endpoints, or internal API functions that were supposed to be protected by authentication gates. This could lead to a complete compromise of user confidentiality and integrity. In web applications using tinyauth for CakePHP-based systems, such a bypass might allow an unauthenticated user to perform actions reserved for administrators, modify database records, or escalate privileges within the application context. The severity is further amplified if these routes expose critical business logic or personal identifiable information that is not independently secured by additional authorization checks at the controller level.
To mitigate this vulnerability, developers must update tinyauth to version 5.1.3 or later where the regular expression matching has been corrected to enforce strict path boundaries. For systems running older versions that cannot be immediately updated, a temporary workaround involves manually modifying the authentication configuration to ensure that route matching is anchored correctly. This can often be achieved by ensuring that any custom regex patterns used for allowed routes include explicit start and end anchors or by switching to exact string comparison methods where feasible. Additionally, it is crucial to implement defense-in-depth strategies by validating permissions not just at the routing layer but also within individual controller actions. Relying solely on middleware-level authentication checks without secondary authorization verification leaves applications vulnerable to such bypass techniques. Regular security audits and static code analysis tools configured to detect unanchored regex patterns in access control logic can help prevent similar issues in future development cycles.
This vulnerability is associated with the MITRE ATT&CK framework under technique T1078: Valid Accounts, as it allows an attacker to leverage valid authentication mechanisms improperly to gain unauthorized access. It also relates to CWE-693: Protection Mechanism Failure because the security control designed to protect specific resources fails due to a logical error in its implementation. Addressing this issue requires not only patching the library but also reviewing other areas of the application where similar regex-based validation might be employed without proper anchoring, ensuring that all access control decisions are robust against substring matching attacks.