Static Web Server (SWS) is a production-ready web server suitable for static web files or assets. In versions 2.1.0 through 2.40.1, a timing-based username enumeration vulnerability in Basic Authentication allows attackers to identify valid users by exploiting early responses for invalid usernames, enabling targeted brute-force or credential-stuffing attacks. SWS checks whether a username exists before verifying the password, causing valid usernames to follow a slower code path (e.g., bcrypt hashing) while invalid usernames receive an immediate 401 response. This timing discrepancy allows attackers to enumerate valid accounts by measuring response-time differences. This issue has been fixed in version 2.41.0.

Affected: crates.io: static-web-server

## Summary

A Timing-based username enumeration in Basic Authentication vulnerability due to early response on invalid usernames could allow attackers to identify valid users and focus their efforts on targeted brute-force or credential-stuffing attacks.

## Details

SWS validates the provided username before performing any password verification. - **Invalid Username:** The server returns a `401 Unauthorized` response immediately. - **Valid Username:** The server proceeds to verify the password (e.g., using `bcrypt`), which introduces a different execution path and measurable timing discrepancy.

This allows an attacker to distinguish between existing and non-existing accounts by analyzing response times.

## PoC

The following statistical results were obtained by measuring the mean response time over 100 iterations using a custom Rust script:

| User Type | Average Response Time | | :--- | :--- | | **Invalid User** | 0.409861 ms | | **Valid User** | 0.250925 ms | | **Difference** | **~0.158936 ms** |

While the valid user responded faster in this specific test environment, the statistically significant gap confirms that the authentication logic does not execute in constant time.

## Impact

Users using the SWS' Basic Authentication feature are primarily impacted.