OWASP Coraza WAF is a golang modsecurity compatible web application firewall library. Prior to 3.3.3, if a request is made on an URI starting with //, coraza will set a wrong value in REQUEST_FILENAME. For example, if the URI //bar/uploads/foo.php?a=b is passed to coraza: , REQUEST_FILENAME will be set to /uploads/foo.php. This can lead to a rules bypass. This vulnerability is fixed in 3.3.3.

Affected: Go: github.com/jptosso/coraza-waf, Go: github.com/corazawaf/coraza/v3

### Summary

URLs starting with `//` are not parsed properly, and the request `REQUEST_FILENAME` variable contains a wrong value, leading to potential rules bypass.

### Details

If a request is made on an URI starting with `//`, coraza will set a wrong value in `REQUEST_FILENAME`. For example, if the URI `//bar/uploads/foo.php?a=b` is passed to coraza: , `REQUEST_FILENAME` will be set to `/uploads/foo.php`.

The root cause is the usage of `url.Parse` to parse the URI in [ProcessURI](https://github.com/corazawaf/coraza/blob/8b612f4e6e18c606e371110227bc7669dc714cab/internal/corazawaf/transaction.go#L768).

`url.Parse` can parse both absolute URLs (starting with a scheme) or relative ones (just the path). `//bar/uploads/foo.php` is a valid absolute URI (the scheme is empty), `url.Parse` will consider `bar` as the host and the path will be set to `/uploads/foo.php`.

### PoC

```go package main

import ( "fmt" "net/url" "os"

"github.com/corazawaf/coraza/v3" )

const testRule = ` SecDebugLogLevel 9 SecDebugLog /dev/stdout SecRule REQUEST_FILENAME "@rx /bar/uploads/.*\.(h?ph(p|tm?l?|ar)|module|shtml)" "id:1,phase:1,deny" `

func main() { var testURL = "//bar/uploads/foo.php"

if os.Getenv("TEST_URL") != "" { testURL = os.Getenv("TEST_URL") }

fmt.Printf("Testing URL: %s\n", testURL)

config := coraza.NewWAFConfig().WithDirectives(testRule)

waf, err := coraza.NewWAF(config)

if err != nil { panic(err) }

tx := waf.NewTransaction()

tx.ProcessURI(testURL, "GET"…

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