Re: Proposal: Stop requiring X-XSS-Protection, require CSP with explanation, for criterion hardened_sites


Dan Kohn
 

I endorse this change.
--
Dan Kohn <dan@...+1-415-233-1000
General Manager, LF Public Health, lfph.io
dankohn.com or book on my calendar: dankohn.com/c



On Tue, Jun 2, 2020 8:49 PM, David Wheeler dwheeler@... wrote:

I propose that for the "hardened_sites" criterion we stop requiring

the HTTP header X-XSS-Protection, and that we require CSP & explain

why.


Here's the background.


The Linux kernel is failing to meet the "hardened sites" criterion:

https://bestpractices.coreinfrastructure.org/en/projects/34?criteria_level=2#hardened_site


The reason is that those sites' HTTP headers do not include something like this:

X-XSS-Protection: 1


The criterion main text is: "The project website, repository (if

accessible via the web), and download site (if separate) MUST include

key hardening headers with nonpermissive values."

with these details: "Note that GitHub is known to meet this. Sites

such as https://securityheaders.io/ can quickly check this. The key

hardening headers are: Content Security Policy (CSP), HTTP Strict

Transport Security (HSTS), X-Content-Type-Options (as "nosniff"),

X-Frame-Options, and X-XSS-Protection. Static web sites with no

ability to log in via the web pages may omit the CSP and

X-XSS-Protection HTTP hardening headers, because in that situation

those headers are less effective."


This issue with the Linux kernel is discussed here:

https://github.com/coreinfrastructure/best-practices-badge/issues/1253


There are two problems. The first is that X-XSS-Protection has not

aged well. It's supposed to enable some heuristic protections. These

protections are largely unnecessary in modern browsers (CSP is

recommended instead), and it's increasingly obvious that this header

will never be standardized. Firefox won't add it, Edge has retired it.

Perhaps most importantly, securityheaders.io doesn't even *report* the

status of X-XSS-Protection, making it suddenly harder to see this

header value for a site... and also providing additional evidence that

X-XSS-Protection has outlived its purpose. Details here:

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-XSS-Protection


The second problem is that while CSP isn't really very helpful on

static sites, it's impractical to detect if a site is a static site or

not, and we very much *do* want to encourage CSP use. So I propose

keeping the main criterion unchanged, but changing these details:


> "Note that GitHub is known to meet this. Sites such as https://securityheaders.io/ can quickly check this. The key hardening headers are: Content Security Policy (CSP), HTTP Strict Transport Security (HSTS), X-Content-Type-Options (as "nosniff"), X-Frame-Options, and X-XSS-Protection. Static web sites with no ability to log in via the web pages may omit the CSP and X-XSS-Protection HTTP hardening headers, because in that situation those headers are less effective."


To the following:


> "Note that GitHub is known to meet this. Sites such as https://securityheaders.io/ can quickly check this. The key hardening headers are: Content Security Policy (CSP), HTTP Strict Transport Security (HSTS), X-Content-Type-Options (as "nosniff"), and X-Frame-Options. In theory static web sites with no ability to log in via the web pages could omit CSP with less risk, because in that situation those headers are less effective. However, there's no reliable way to detect that a site is fully static, so we simply require CSP for all such sites."


--- David A. Wheeler

Director of Open Source Supply Chain Security, The Linux Foundation




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