CVE-2026-109167 in TDuck Survey Form
Summary
by MITRE • 10/12/2026
TDuck survey form through 6.0 contains an insecure direct object reference vulnerability in the saveFormTheme handler that allows authenticated users to overwrite other users' form themes. Attackers whose form has no theme can submit another form's sequential theme id with their own formKey, replacing its colours and image URLs and removing the victim's theme.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified as an insecure direct object reference within TDuck survey forms version 6.0 represents a critical flaw in access control logic, specifically located in the saveFormTheme handler. This type of vulnerability arises when an application exposes internal implementation objects, such as database keys or file names, to users without performing adequate authorization checks. In this specific context, the system relies on sequential integer identifiers for form themes rather than opaque, randomly generated tokens that are difficult to predict or enumerate. The core technical flaw lies in the server-side processing of requests where the application accepts a theme identifier provided by the client and applies it directly to the target resource without verifying whether the authenticated user submitting the request actually owns or has permission to modify that specific form's theme configuration.
From an operational perspective, this lack of object-level authorization allows any authenticated user to manipulate the visual presentation and branding elements of other users' surveys. By exploiting the sequential nature of the theme identifiers, an attacker can iterate through potential IDs while supplying their own valid session credentials and a legitimate formKey associated with their account or another target they control. The attack vector involves submitting a request that pairs the victim's theme ID with the attacker's configuration data, effectively overwriting the original colors and image URLs defined in the victim's theme. This results in the complete removal of the victim's custom branding and its replacement with the attacker's chosen aesthetic settings, which can be used for phishing campaigns or to cause significant reputational damage by making legitimate surveys appear malicious or unprofessional.
The impact extends beyond mere cosmetic changes; it undermines the integrity and trustworthiness of the survey platform. Since TDuck is often utilized for data collection where brand consistency is crucial, this vulnerability allows an attacker to deface content in a way that may confuse respondents or erode confidence in the legitimacy of the surveys being conducted. Furthermore, if the theme images include external URLs controlled by the attacker, it could potentially lead to further risks such as cross-site scripting if those resources are rendered without proper sanitization, although the primary documented impact is the unauthorized modification of configuration data. This scenario highlights a common failure in web application security where authentication (verifying who the user is) is conflated with authorization (determining what that user can do), leading to privilege escalation at the object level rather than the role level.
To mitigate this vulnerability, developers must implement strict access control checks within the saveFormTheme handler. The system should verify that the authenticated user making the request owns the form associated with the theme ID being modified before allowing any updates to proceed. This can be achieved by querying the database to confirm a relationship between the current session's user account and the target form or theme resource, ensuring that only authorized entities can alter these settings. Additionally, replacing sequential integer identifiers for themes with universally unique identifiers (UUIDs) would significantly increase the difficulty of enumeration attacks, although this is not a substitute for proper authorization logic. Input validation should also be enforced to ensure that all submitted parameters are within expected ranges and formats, reducing the attack surface associated with malformed or maliciously crafted requests.
This vulnerability aligns closely with CWE-639, which describes Injection of Critical Data via Direct Object Reference, as it involves manipulating an object identifier to access or modify data belonging to another user. In terms of offensive security frameworks, this behavior is characteristic of the ATT&CK technique T1078, specifically Valid Accounts and potentially T1534 if used for internal spear-phishing by defacing legitimate communications. Addressing these issues requires a shift toward principle-of-least-privilege design patterns where every request that modifies state must explicitly validate ownership or permission rights before execution. Regular security audits focusing on API endpoints and form handlers are essential to identify similar flaws in other parts of the application, ensuring that all user-supplied identifiers are treated as untrusted input until their association with the requesting entity is cryptographically or logically proven.