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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It's unfortunate they started permitting using other directives while not actually supporting it or fixing all the terrible issues occurring when you do. It's fine inside location blocks as long as you follow that rule and it's broken outside location blocks too if you don't.
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For example, their documentation on that talks about how you should use server blocks, location blocks, try_files, etc. instead of if directives for better performance, readability and ease of doing things correctly. Often you do need if directives to do things properly though.
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Using try_files is less efficient than doing things without it in many cases because it checks for the existence of each file including the last one before handling it as another request. Some of the suggestions on using it are quite inefficient and could be done better using if.