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CVE-2026-27480: Tick-Tock: Cracking Static Web Server via Timing Side-Channels

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Tick-Tock: Cracking Static Web Server via Timing Side-Channels

Vulnerability ID: CVE-2026-27480
CVSS Score: 5.3
Published: 2026-02-20

A classic timing-based side-channel vulnerability in Static Web Server (SWS) allows remote attackers to enumerate valid usernames. By measuring the microsecond-level differences in response times during Basic Authentication, adversaries can distinguish between 'User Not Found' and 'User Found, Password Wrong' states, effectively bypassing the first layer of authentication defense.

TL;DR

Static Web Server (SWS) < 2.41.0 optimized its Basic Auth too much. It checked usernames first and returned early if they didn't exist. This logic created a timing discrepancy: invalid users returned instantly (or with a specific timing profile), while valid users triggered the slow hashing mechanism (or a different profile). Attackers can stopwatch the server to harvest valid usernames.

⚠️ Exploit Status: POC

Technical Details

  • CWE ID: CWE-204 (Observable Response Discrepancy)
  • CVSS v3.1: 5.3 (Medium)
  • Attack Vector: Network (Remote)
  • Attack Complexity: Low (Statistical)
  • Impact: Confidentiality (User Enumeration)
  • Exploit Status: Proof-of-Concept Available

Affected Systems

  • Static Web Server (SWS) < 2.41.0
  • static-web-server: < 2.41.0 (Fixed in: 2.41.0)

Code Analysis

Commit: 7bf0fd4

Fix timing based username enumeration in basic auth

Diff shows removal of early return and implementation of unconditional bcrypt_verify
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Exploit Details

  • GitHub Advisory: Statistical analysis of response times proving enumeration possibility

Mitigation Strategies

  • Upgrade to version 2.41.0 immediately.
  • Implement aggressive rate limiting to thwart statistical analysis.
  • Use strong, high-entropy passwords to mitigate the subsequent brute-force risk.
  • Monitor logs for high-frequency 401 responses from single IPs.

Remediation Steps:

  1. Stop the SWS service.
  2. Download the latest binary (v2.41.0+) or pull the latest Docker image.
  3. Replace the executable.
  4. Restart the service.
  5. Verify the version using static-web-server --version.

References

Read the full report for CVE-2026-27480 on our website for more details including interactive diagrams and full exploit analysis.

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