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fix: check escaped backslashes on Windows - #2810
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Caddy's path matchers whose pattern contains "%" read a backslash as "%2f" on Windows, which they do not resolve as a separator. Go escapes a backslash even when RawPath is empty, so the escaped-path check skipped "/public/tool.php%5C..%5C..%5Cadmin%5Ctool.php": a "/public/%*" rule matched it, but admin/tool.php ran. The check now also runs when the path contains a backslash on Windows, and folds backslashes into separators before comparing, so legitimate paths such as "/dir\index.php" are no longer rejected with a 400.
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Security fix (Windows only). Follow-up to 393e007.
On Windows, Caddy path matchers whose pattern contains
%read a backslash as%2f, which they do not resolve as a separator. Go escapes a backslash even whenRawPathis empty, soescapedPathSelectsAnotherScriptreturned early for/public/tool.php%5C..%5C..%5Cadmin%5Ctool.php: a/public/%*rule matched it, butadmin/tool.phpran.The check now also runs when the path contains a backslash on Windows. Backslashes are folded into separators before comparing, which also fixes a regression: legitimate paths such as
/dir\index.phpwere rejected with a 400.Found while porting the fix to Caddy: caddyserver/caddy#8357
Assistance Disclosure
Claude Code (Claude Opus 5.5) found the issue while porting the fix to Caddy, and wrote the patch and tests. I reviewed and tested the result.