lowSeverity: lowRisk ratingHow usable this gap is to an attacker. Severity sets the posture penalty: critical −40, high −20, medium −10, low −4, info −1. Higher severity means fix it sooner.Netlify headersWhere it livesImplementationThis fix is applied in: Netlify headers. That's the surface you'll edit, DNS, response headers, or a static file.~2 minTime to fixEffortRoughly 2 minutes of hands-on work, propagation aside. Most of these are copy-paste.+4 posture+4 postureScore impactPoints this fix recovers in the ApeCyber posture score (0–100). Posture = 100 minus the severity penalty of every open finding; clearing this finding adds these points back.

X-XSS-Protection: turn the legacy header OFF

The old anti-XSS header now introduces bugs, set it to 0

The threat

X-XSS-Protection: 1; mode=block looks protective, but it’s a deprecated header driving a long-removed browser feature. In some older browsers its filter could itself be abused to create information-leak and false-positive vulnerabilities. Modern guidance is unambiguous: turn it off and rely on a real Content-Security-Policy instead.

The exact fix

Set the header to 0 (or remove it entirely). On Netlify:

# netlify.toml
[[headers]]
  for = "/*"
  [headers.values]
    X-XSS-Protection = "0"

Or in _headers:

/*
  X-XSS-Protection: 0

That’s it. Your actual XSSXSSAttackCross-Site Scripting: an attack that injects attacker-controlled JavaScript into your page to steal sessions, keylog, or act as the user. A strong CSP is the primary defense. protection comes from CSPCSPHTTP headerContent-Security-Policy: a response header that whitelists exactly which scripts, styles, images and connections a page may use, so an injected payload simply has no permission to run., this header just needed to stop sending a harmful legacy value.

Verify it

curl -sI https://yourdomain.com | grep -i x-xss

Expected:

x-xss-protection: 0

Proof

A two-minute, one-line change on dev3lop.com, flipping 1; mode=block to 0, cleared the finding cleanly as part of the climb to grade A.