H3 is a minimal H(TTP) framework. Versions 2.0.1-beta.0 through 2.0.0-rc.8 contain a Timing Side-Channel vulnerability in the requireBasicAuth function due to the use of unsafe string comparison (!==). This allows an attacker to deduce the valid password character-by-character by measuring the server's response time, effectively bypassing password complexity protections. This issue is fixed in version 2.0.1-rc.9.

Affected: npm: h3

### Summary A Timing Side-Channel vulnerability exists in the `requireBasicAuth` function due to the use of unsafe string comparison (`!==`). This allows an attacker to deduce the valid password character-by-character by measuring the server's response time, effectively bypassing password complexity protections.

### Details The vulnerability is located in the `requireBasicAuth` function. The code performs a standard string comparison between the user-provided password and the expected password:

~~~typescript if (opts.password && password !== opts.password) { throw autheFailed(event, opts?.realm); } ~~~

In V8 (and most runtime environments), the `!==` operator is optimized to "fail fast." It stops execution and returns `false` as soon as it encounters the first mismatched byte. * If the first character is wrong, it returns immediately. * If the first character is correct but the second is wrong, it takes slightly longer.

By statistically analyzing these minute timing differences over many requests, an attacker can determine the correct password one character at a time.

### PoC This vulnerability is exploitable in real-world scenarios without direct access to the server machine.

To reproduce this, an attacker can send two packets (or bursts of packets) at the exact same time: 1. **Packet A:** Contains a password that is known to be incorrect starting at the first character (e.g., `AAAA...`). 2. **Packet B:** Contains a password where the first character is a guess (e…