Impact Analysis

This vulnerability allows a remote attacker to recover valid passwords by exploiting timing differences in the authentication process. By deducing the password character-by-character, the attacker can bypass password complexity protections and gain unauthorized access.

The attack is feasible especially in low-latency environments such as local networks or cloud setups where the attacker is co-located with the target server.

The impact is primarily on confidentiality, as unauthorized access to systems or data can occur without affecting integrity or availability.

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Compliance Impact

I don't know

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Executive Summary

[{'type': 'paragraph', 'content': "CVE-2026-33129 is a timing side-channel vulnerability in the requireBasicAuth function of the h3js/h3 framework versions 2.0.1-beta.0 through 2.0.0-rc.8. The vulnerability arises because the function uses an unsafe string comparison operator (!==) that performs a byte-by-byte comparison and returns immediately upon the first mismatch. This behavior causes the server's response time to vary depending on how many initial characters of the password are correct."}, {'type': 'paragraph', 'content': 'An attacker can exploit this timing difference by sending multiple authentication requests with different password guesses and measuring the response times. By statistically analyzing these timings, the attacker can deduce the valid password one character at a time, effectively bypassing password complexity protections.'}, {'type': 'paragraph', 'content': 'The issue was fixed in version 2.0.1-rc.9 by implementing a constant-time string comparison function and adding random jitter delays to authentication failure responses to prevent timing analysis.'}] [1, 3]

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Detection Guidance

[{'type': 'paragraph', 'content': "This vulnerability can be detected by observing timing discrepancies in the server's response times during basic authentication attempts. An attacker or tester can send multiple authentication requests with different password guesses and measure the time-to-first-byte or overall response time to identify if the server leaks information about password correctness character-by-character."}, {'type': 'paragraph', 'content': 'To detect this on your system, you can use network analysis tools or scripting to send repeated authentication requests and measure response times. For example, using curl in a loop with different passwords and measuring response times, or using tools like Wireshark or tcpdump to capture and analyze timing patterns.'}, {'type': 'list_item', 'content': 'Use curl with timing output to measure response times for different password guesses: `curl -w "%{time_starttransfer}\\n" -o /dev/null -s -u user:password_guess http://target`'}, {'type': 'list_item', 'content': 'Use a scripting language (e.g., Python) to automate multiple requests with varying passwords and statistically analyze response times.'}, {'type': 'list_item', 'content': 'Capture network traffic with Wireshark or tcpdump and analyze timing differences between authentication attempts.'}] [3]

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Mitigation Strategies

The primary mitigation is to upgrade the h3 package to version 2.0.1-rc.9 or later, where the vulnerability is fixed by implementing constant-time string comparison and adding random jitter delays to authentication failure responses.

If upgrading immediately is not possible, consider implementing additional network-level protections such as rate limiting authentication attempts and monitoring for suspicious timing-based attack patterns.

The fix includes replacing unsafe string comparisons with a timing-safe comparison function and introducing randomized delays to prevent attackers from inferring password characters through timing analysis.

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