Explicit disable (unsafe) X-XSS-Protection-header
#751
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A bit counter-intuitive, but `X-XSS-Protection` is actually dangerous on (old) browsers supporting the spec. In _filtering_ mode it easily allows attackers to remove critical blocks of JavaScript, which can introduce vulnerabilities in otherwise safe code: [PoC](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-XSS-Protection#vulnerabilities_caused_by_xss_filtering). In _blocking_ mode it can be used as an side-channel oracle, leaking cross origin bodies/tokens: [theory](https://portswigger.net/research/abusing-chromes-xss-auditor-to-steal-tokens) / [PoC](https://www.youtube.com/watch?v=HcrQy0C-hEA) Hot take, this is a terrible header that shouldn't be included. In this PR I explicit disable it, but this PR could also easily be refactored to completely remove the header. Disabling it on modern browsers does nothing, as it is already disabled.
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A bit counter-intuitive, but
X-XSS-Protectionis actually dangerous on (old) browsers supporting the spec.In filtering mode it easily allows attackers to remove critical blocks of JavaScript, which can introduce vulnerabilities in otherwise safe code: PoC.
In blocking mode it can be used as an side-channel oracle, leaking cross origin bodies/tokens: theory / PoC
Hot take, this is a terrible header that shouldn't be included. In this PR I explicit disable it, but this PR could also easily be refactored to completely remove the header.
Disabling it on modern browsers does nothing, as it is already disabled.