CVE-2026-27480 is a medium-severity (CVSS 5.3) CWE-204 vulnerability in static-web-server. A fix is available for static-web-server — see the affected versions and patch details below.
Static Web Server: Timing-Based Username Enumeration in Basic Authentication
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-27480.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-27480 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
static-web-serverReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
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 Unauthorizedresponse 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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | static-web-server | ≥ 2.1.0&&< 2.41.0 | 2.41.0cargo update -p static-web-server --precise 2.41.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for static-web-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update static-web-server to 2.41.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27480 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-27480 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-27480. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-27480 in your dependencies?
O3 Security finds CVE-2026-27480 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.