External risk intelligence

UserSpice Username Enumeration Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.3)

CVE-2018-25350

UserSpice is a web application framework. The vulnerable endpoint, existingUsernameCheck.php, is a web-based script designed to be accessed via POST requests. As a web application component, this functionality is commonly exposed to the internet in public-facing deployments to facilitate user account interactions.

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This advisory concerns a username enumeration vulnerability in UserSpice, a web application framework. The vulnerability allows unauthenticated attackers to discover valid usernames by analyzing the application's responses to specific requests. The primary concern is confirming if our systems utilize the affected UserSpice versions and if this specific functionality is exposed.

Attackers can find valid usernames.
Confirms relevance and potential exposure of UserSpice.
Assess UserSpice use and exposure.

Attack Path

How an attacker could exploit the issue

An attacker can discover valid usernames by sending specially crafted POST requests to a web application's `existingUsernameCheck.php` endpoint. By analyzing the responses, they can determine which submitted usernames are already in use within the system. This exposure could enable further attacks targeting valid accounts.

No authentication required.
Submit usernames to check endpoint.
Enumerate valid user accounts.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow unauthenticated attackers to discover valid usernames on systems where userSpice is deployed and the `existingUsernameCheck.php` endpoint is accessible. By analyzing the responses to POST requests containing potential usernames, attackers may identify existing accounts within the application.

Valid usernames could be exposed.
Username enumeration via POST requests.
Facilitates further targeted attacks.

Operational Fix

Recommended remediation, mitigation, and detection steps

The application owner is likely responsible for addressing this username enumeration vulnerability in UserSpice, as it affects a core web application function. The first practical move is to identify all instances of UserSpice, determine their exposure and business criticality, and then locate the accountable owner for remediation planning.

Identify affected UserSpice instances.
Verify exposure and criticality.
Plan remediation based on risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is UserSpice?

UserSpice is a PHP-based web application framework designed to help developers build secure user authentication and management systems. It provides pre-built components for handling member logins, password resets, and user account profiles. By offering these ready-to-use tools, it allows teams to quickly deploy web applications that require user registration and access control features.

What is the username enumeration vulnerability in CVE-2018-25350?

This vulnerability, classified as CWE-204 (Observable Response Discrepancy), allows unauthorized users to verify if a specific username exists in the system. The application reacts differently when a submitted username is already taken compared to one that is not. By observing these predictable response patterns, an attacker can systematically confirm valid account names, which serves as a foundation for more targeted follow-up attacks.

How does an attacker trigger this vulnerability?

An attacker sends a series of automated POST requests to the `existingUsernameCheck.php` file on the server. By inspecting the server's response text for specific markers like the 'taken' string, they can validate account existence. This flaw does not require the attacker to be logged in, but it is only triggered when the application is configured to allow these username validation checks to be queried remotely.

Is my system at risk according to Halo Surface Signal?

Halo Surface Signal identifies this as a potential risk because the affected script is a web-based component frequently exposed to the public internet to enable interactive user registration. If your instance of UserSpice is internet-facing, this endpoint is likely reachable by any remote actor, making it easier for them to enumerate users without needing internal network access.

What should I do if I am running UserSpice?

Your first step is to perform an inventory to locate all instances of UserSpice within your environment and determine which ones are accessible over the internet. Once mapped, assess the business criticality of those specific systems. Reach out to the application owners to document these findings and coordinate a plan to restrict or modify the vulnerable check functionality.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.