Without nosniff a browser may MIME-sniff a response and execute a file the server declared as something inert.
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How this rule is weighted
- Importance
- 5 / 10
- How much this matters relative to other rules.
- Confidence
- SPECIFICATION
- A standard says so: HTML, WCAG, an RFC or Google's own documentation.
- Severity
- warning
- How the finding is presented when it fails.
- Scoring
- Counts
- A failure costs points in its category.
Impact is importance multiplied by the confidence tier’s weight — SPECIFICATION 1.0, RESEARCH 0.7, EMERGING 0.3, EXPERIMENTAL 0.1. Two rules backed by the same class of evidence therefore always carry the same weight, which is what makes the score reproducible rather than hand-tuned.
Questions about this rule
- Does SEC_X_CONTENT_TYPE_OPTIONS affect my score?
- Yes. It is an importance 5 rule at SPECIFICATION confidence, so a failure costs 5 × 1 points of impact in the Security category before that category is normalised to 100.
- What does SPECIFICATION confidence mean?
- A standard says so: HTML, WCAG, an RFC or Google's own documentation. Confidence is a declared tier rather than a per-rule number, so every rule backed by the same class of evidence carries the same weight - which is what makes the score reproducible instead of hand-tuned.
- How do I check SEC_X_CONTENT_TYPE_OPTIONS on my own site?
- Paste your URL into the box above and it runs only this rule, usually in a couple of seconds. It is also included in the Security checker and in a full scan.
Tags
- security
- headers
Related Security rules
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- Site is served over HTTPSThe page must be served over HTTPS, not plain HTTP.SEC_HTTPS
- Certificate covers the hostname being servedChecks the scanned hostname against the certificate's subject alternative names, including wildcard entries. A certificate that does not cover the hostname triggers the same interstitial as an expired one, and it is easy to miss when the apex and www forms are configured separately.SEC_TLS_HOSTNAME_COVERED
- No passwords submitted via GETA GET form puts the password in the URL, where it lands in browser history, server logs and referrer headers.SEC_FORM_METHOD_GET_SENSITIVE
- Certificate is not close to expiryReads the leaf certificate's expiry date from the handshake. An expired certificate blocks the entire site behind an interstitial, and because renewal is usually automated, the failure mode is silent right up until it is total.SEC_TLS_CERT_NOT_EXPIRING
- Connection negotiates TLS 1.2 or betterReports the protocol version actually negotiated. RFC 8996 deprecated TLS 1.0 and 1.1 in 2021; browsers now warn or refuse outright, and PCI DSS has prohibited them for card handling since 2018.SEC_TLS_PROTOCOL_MODERN