The configuration directives are still vulnerable and can still be easily used in a way that allows an attacker to inject headers for HTTP/1.1.
Their fixes forbid spaces and control characters in request URI, header names and Host header so most sources of tainted data are gone.
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Previously, incredibly pervasive nginx configurations simply using a regex location block with a capture like (.*) and then passing it to one of many directives like return were vulnerable to header injection. Many answers on Stack Overflow, blog posts, etc. have vulnerable code.
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You can find many examples of Stack Overflow answers proposing vulnerable configurations with simple searches:
"return 301 $uri" site:stackoverflow.com
These vulnerabilities are pervasive in nginx configurations and they strangely don't mention this in any official docs.
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So imo it's insane that this even needed to be developed, but Yandex made a static analysis tool for Nginx configurations, and one of its rules spots and warns against this:
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Yeah, we use it for GrapheneOS.
It's unfortunately not maintained anymore and bitrotted due to a major pyparsing update. It doesn't work anymore unless you force holding back the update.
It'll be a bit annoying to use now that the main tainted input sources have strict checks.
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It's unfortunate directives like return are still vulnerable.
Most vulnerable configuration will be fixed by people updating to 1.21 / 1.22 but there will still be plenty of vulnerabilities.
It's unfortunate they don't even mention those directives don't do escaping in docs.
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> It'll be a bit annoying to use now that the main tainted input sources have strict checks.
What do you mean, how does that make Gixy more annoying to use? Do you mean that it would now have false positives due to better Nginx behavior?
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Their statements about the if directive are problematic because they should be telling people what's safe and what isn't separately from documenting best practices for performance / style. It's fine to use it if it only contains return/rewrite directive. Other stuff is broken.
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Their best course of action would probably be to outright refuse to load a configuration that uses the unsafe directives in that context, honestly. But who knows if they'd actually do that. :/
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There are a few examples of completely correct and sensible usage of if directives in github.com/GrapheneOS/gra and our other nginx configurations.
#1 is safely removing double slashes in a single redirect which is important for SEO to avoid having multiple locations for content.
Has to be if directive since otherwise we'd have to stop using exact matches and high priority prefix matches.
#2 is serving SVG favicon based on accept header for /favicon.ico which we use for dark theme support. Unfortunately temporarily broken due to bugs.chromium.org/p/chromium/iss.
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#3 is to efficiently redirect /path/ to /path if /path.html exists. We do that to deal with many cases of backlinks adding an incorrect trailing slash. It also handles all cases where we turned a leaf page into a directory without needing to hard-wire redirects for each forever.
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