Defaults.Exposed › Methodology › v7 registry › MIME-sniffing protection
MIME-sniffing protection
Methodology v7 · canonical ID x-content-type-options · Web Security · scored · census as of July 28, 2026
Stops browsers mis-reading files in ways attackers can abuse.
Definition
| Canonical ID | x-content-type-options |
|---|---|
| Category | Web Security |
| Grade impact | Scored — counts toward the grade |
| Pass | The site sends X-Content-Type-Options: nosniff. |
| Fail | The header is absent. |
| Example (passing) | X-Content-Type-Options: nosniff |
No-data rule: when this check couldn't be determined for a domain (timeout, SERVFAIL, redacted
source) it returns N/A and is excluded from that domain's scoring denominator — "couldn't determine"
is never counted as a failure. "Determined absent" is a real fail.
Prevalence across the census
7.28% of graded domains send X-Content-Type-Options: nosniff (20,058,145 of 275,666,275, as of July 28, 2026).
Census denominator: 275,666,275 graded domains. Aggregates only — never an individual domain's result.
Fix it
Plain-English impact, cost of ignoring it, and step-by-step remediation: defaults.exposed/en/fix/mime-sniffing
Cite this check
Defaults.Exposed, "MIME-sniffing protection (x-content-type-options)", Grading Methodology v7 (census as of July 28, 2026). https://defaults.exposed/methodology/v7/x-content-type-options
Permalink: https://defaults.exposed/methodology/v7/x-content-type-options ·
All 34 checks: v7 registry ·
Machine-readable: checks.json ·
Licence: open data