CWE-204: Observable Response Discrepancy

The product provides different responses to incoming requests in a way that reveals internal state information to an unauthorized actor outside of the intended control sphere.

Consequences

• Confidentiality, Access Control: Read Application Data, Bypass Protection Mechanism

How to prevent it

• Architecture and Design: Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
• Implementation: Ensure that error messages only contain minimal details that are useful to the intended audience and no one else. The messages need to strike the balance between being too cryptic (which can confuse users) or being too detailed (which may reveal more than intended). The messages should not reveal the methods that were used to determine the error. Attackers can use detailed information to refine or optimize their original attack, thereby increasing their chances of success. If errors must be captured in some detail, record them in log messages, but consider what could occur if the log messages can be viewed by attackers. Highly sensitive information such as passwords should never be saved to log files. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a user account exists or not.

Recent advisories

• GHSA-mfxh-vp55-7gc6 — Contao: The registration module re-sends activation mails
• GHSA-8fxq-53rx-ph5f — Coder: Login endpoint user enumeration via timing-defense placeholder in password comparison
• GHSA-4vpg-gwqq-w44c — SiYuan: 17 block metadata/content endpoints in kernel/api/block.go have zero publish-access filtering, reachable by anonymous publish-mode readers
• GHSA-cr7p-cr3q-h5cm — Budibase: Account Enumeration via Login Lockout Response Differential
• GHSA-chgm-3698-jm42 — Ghost: Member existence leak via magic link sign-in response
• GHSA-vpfx-pxqw-2w79 — AVideo CVE-2026-43881 incomplete fix - `objects/mention.json.php:17` is an unauthenticated user enumeration sibling that survives `d9cdc7024`
• GHSA-m24v-f7g5-gq67 — Statamic CMS vulnerable to email enumeration via forgot password endpoint
• GHSA-m99f-mmvg-3xmx — AVideo has Pre-Captcha User Enumeration and Account Status Disclosure in Password Recovery Endpoint
• GHSA-h29g-q5c2-9h4f — Parse Server email verification resend page leaks user existence
• GHSA-gqc5-xv7m-gcjq — Shopware has user enumeration via distinct error codes on Store API login endpoint
• GHSA-w54v-hf9p-8856 — Parse Server vulnerable to user enumeration via email verification endpoint
• GHSA-387m-j3p9-3php — NocoDB Vulnerable to User Enumeration via Password Reset Endpoint
• GHSA-654x-9q7r-g966 — CI4MS Vulnerable to User Email Enumeration via Password Reset Flow
• GHSA-pvm5-9frx-264r — Zitadel has a user enumeration vulnerability in Login UIs
• GHSA-pc73-rj2c-wvf9 — Gitea's /api/v1/user endpoint has different responses for failed authentication depending on whether a username exists

All advisories for CWE-204