Merge commit from fork

* fix: FastCGI split SCRIPT_NAME/PATH_INFO confusion

* fix comment

modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go

@@ -16,6 +16,7 @@ package fastcgi
 
 import (
 	"crypto/tls"
+	"errors"
 	"fmt"
 	"net"
 	"net/http"
@@ -23,9 +24,12 @@ import (
 	"strconv"
 	"strings"
 	"time"
+	"unicode/utf8"
 
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
+	"golang.org/x/text/language"
+	"golang.org/x/text/search"
 
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
@@ -33,7 +37,11 @@ import (
 	"github.com/caddyserver/caddy/v2/modules/caddytls"
 )
 
-var noopLogger = zap.NewNop()
+var (
+	ErrInvalidSplitPath = errors.New("split path contains non-ASCII characters")
+
+	noopLogger = zap.NewNop()
+)
 
 func init() {
 	caddy.RegisterModule(Transport{})
@@ -50,6 +58,9 @@ type Transport struct {
 	// actual resource (CGI script) name, and the second piece will be set to
 	// PATH_INFO for the CGI script to use.
 	//
+	// Split paths can only contain ASCII characters.
+	// Comparison is case-insensitive.
+	//
 	// Future enhancements should be careful to avoid CVE-2019-11043,
 	// which can be mitigated with use of a try_files-like behavior
 	// that 404s if the fastcgi path info is not found.
@@ -109,6 +120,28 @@ func (t *Transport) Provision(ctx caddy.Context) error {
 		t.DialTimeout = caddy.Duration(3 * time.Second)
 	}
 
+	var b strings.Builder
+
+	for i, split := range t.SplitPath {
+		b.Grow(len(split))
+
+		for j := 0; j < len(split); j++ {
+			c := split[j]
+			if c >= utf8.RuneSelf {
+				return ErrInvalidSplitPath
+			}
+
+			if 'A' <= c && c <= 'Z' {
+				b.WriteByte(c + 'a' - 'A')
+			} else {
+				b.WriteByte(c)
+			}
+		}
+
+		t.SplitPath[i] = b.String()
+		b.Reset()
+	}
+
 	return nil
 }
 
@@ -385,8 +418,15 @@ func (t Transport) buildEnv(r *http.Request) (envVars, error) {
 	return env, nil
 }
 
+var splitSearchNonASCII = search.New(language.Und, search.IgnoreCase)
+
 // splitPos returns the index where path should
 // be split based on t.SplitPath.
+//
+// example: if splitPath is [".php"]
+// "/path/to/script.php/some/path": ("/path/to/script.php", "/some/path")
+//
+// Adapted from FrankenPHP's code (copyright 2026 Kévin Dunglas, MIT license)
 func (t Transport) splitPos(path string) int {
 	// TODO: from v1...
 	// if httpserver.CaseSensitivePath {
@@ -396,12 +436,54 @@ func (t Transport) splitPos(path string) int {
 		return 0
 	}
 
-	lowerPath := strings.ToLower(path)
+	pathLen := len(path)
+
+	// We are sure that split strings are all ASCII-only and lower-case because of validation and normalization in Provision().
 	for _, split := range t.SplitPath {
-		if idx := strings.Index(lowerPath, strings.ToLower(split)); idx > -1 {
-			return idx + len(split)
+		splitLen := len(split)
+
+		for i := 0; i < pathLen; i++ {
+			if path[i] >= utf8.RuneSelf {
+				if _, end := splitSearchNonASCII.IndexString(path, split); end > -1 {
+					return end
+				}
+
+				break
+			}
+
+			if i+splitLen > pathLen {
+				continue
+			}
+
+			match := true
+			for j := 0; j < splitLen; j++ {
+				c := path[i+j]
+
+				if c >= utf8.RuneSelf {
+					if _, end := splitSearchNonASCII.IndexString(path, split); end > -1 {
+						return end
+					}
+
+					break
+				}
+
+				if 'A' <= c && c <= 'Z' {
+					c += 'a' - 'A'
+				}
+
+				if c != split[j] {
+					match = false
+
+					break
+				}
+			}
+
+			if match {
+				return i + splitLen
+			}
 		}
 	}
+
 	return -1
 }
 

modules/caddyhttp/reverseproxy/fastcgi/fastcgi_test.go

@@ -0,0 +1,246 @@
+package fastcgi
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/caddyserver/caddy/v2"
+)
+
+func TestProvisionSplitPath(t *testing.T) {
+	tests := []struct {
+		name          string
+		splitPath     []string
+		wantErr       error
+		wantSplitPath []string
+	}{
+		{
+			name:          "valid lowercase split path",
+			splitPath:     []string{".php"},
+			wantErr:       nil,
+			wantSplitPath: []string{".php"},
+		},
+		{
+			name:          "valid uppercase split path normalized",
+			splitPath:     []string{".PHP"},
+			wantErr:       nil,
+			wantSplitPath: []string{".php"},
+		},
+		{
+			name:          "valid mixed case split path normalized",
+			splitPath:     []string{".PhP", ".PHTML"},
+			wantErr:       nil,
+			wantSplitPath: []string{".php", ".phtml"},
+		},
+		{
+			name:          "empty split path",
+			splitPath:     []string{},
+			wantErr:       nil,
+			wantSplitPath: []string{},
+		},
+		{
+			name:      "non-ASCII character in split path rejected",
+			splitPath: []string{".php", ".Ⱥphp"},
+			wantErr:   ErrInvalidSplitPath,
+		},
+		{
+			name:      "unicode character in split path rejected",
+			splitPath: []string{".phpⱥ"},
+			wantErr:   ErrInvalidSplitPath,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tr := Transport{SplitPath: tt.splitPath}
+			err := tr.Provision(caddy.Context{})
+
+			if tt.wantErr != nil {
+				require.ErrorIs(t, err, tt.wantErr)
+
+				return
+			}
+
+			require.NoError(t, err)
+			assert.Equal(t, tt.wantSplitPath, tr.SplitPath)
+		})
+	}
+}
+
+func TestSplitPos(t *testing.T) {
+	tests := []struct {
+		name      string
+		path      string
+		splitPath []string
+		wantPos   int
+	}{
+		{
+			name:      "simple php extension",
+			path:      "/path/to/script.php",
+			splitPath: []string{".php"},
+			wantPos:   19,
+		},
+		{
+			name:      "php extension with path info",
+			path:      "/path/to/script.php/some/path",
+			splitPath: []string{".php"},
+			wantPos:   19,
+		},
+		{
+			name:      "case insensitive match",
+			path:      "/path/to/script.PHP",
+			splitPath: []string{".php"},
+			wantPos:   19,
+		},
+		{
+			name:      "mixed case match",
+			path:      "/path/to/script.PhP/info",
+			splitPath: []string{".php"},
+			wantPos:   19,
+		},
+		{
+			name:      "no match",
+			path:      "/path/to/script.txt",
+			splitPath: []string{".php"},
+			wantPos:   -1,
+		},
+		{
+			name:      "empty split path",
+			path:      "/path/to/script.php",
+			splitPath: []string{},
+			wantPos:   0,
+		},
+		{
+			name:      "multiple split paths first match",
+			path:      "/path/to/script.php",
+			splitPath: []string{".php", ".phtml"},
+			wantPos:   19,
+		},
+		{
+			name:      "multiple split paths second match",
+			path:      "/path/to/script.phtml",
+			splitPath: []string{".php", ".phtml"},
+			wantPos:   21,
+		},
+		// Unicode case-folding tests (security fix for GHSA-g966-83w7-6w38)
+		// U+023A (Ⱥ) lowercases to U+2C65 (ⱥ), which has different UTF-8 byte length
+		// Ⱥ: 2 bytes (C8 BA), ⱥ: 3 bytes (E2 B1 A5)
+		{
+			name:      "unicode path with case-folding length expansion",
+			path:      "/ȺȺȺȺshell.php",
+			splitPath: []string{".php"},
+			wantPos:   18, // correct position in original string
+		},
+		{
+			name:      "unicode path with extension after expansion chars",
+			path:      "/ȺȺȺȺshell.php/path/info",
+			splitPath: []string{".php"},
+			wantPos:   18,
+		},
+		{
+			name:      "unicode in filename with multiple php occurrences",
+			path:      "/ȺȺȺȺshell.php.txt.php",
+			splitPath: []string{".php"},
+			wantPos:   18, // should match first .php, not be confused by byte offset shift
+		},
+		{
+			name:      "unicode case insensitive extension",
+			path:      "/ȺȺȺȺshell.PHP",
+			splitPath: []string{".php"},
+			wantPos:   18,
+		},
+		{
+			name:      "unicode in middle of path",
+			path:      "/path/Ⱥtest/script.php",
+			splitPath: []string{".php"},
+			wantPos:   23, // Ⱥ is 2 bytes, so path is 23 bytes total, .php ends at byte 23
+		},
+		{
+			name:      "unicode only in directory not filename",
+			path:      "/Ⱥ/script.php",
+			splitPath: []string{".php"},
+			wantPos:   14,
+		},
+		// Additional Unicode characters that expand when lowercased
+		// U+0130 (İ - Turkish capital I with dot) lowercases to U+0069 + U+0307
+		{
+			name:      "turkish capital I with dot",
+			path:      "/İtest.php",
+			splitPath: []string{".php"},
+			wantPos:   11,
+		},
+		// Ensure standard ASCII still works correctly
+		{
+			name:      "ascii only path with case variation",
+			path:      "/PATH/TO/SCRIPT.PHP/INFO",
+			splitPath: []string{".php"},
+			wantPos:   19,
+		},
+		{
+			name:      "path at root",
+			path:      "/index.php",
+			splitPath: []string{".php"},
+			wantPos:   10,
+		},
+		{
+			name:      "extension in middle of filename",
+			path:      "/test.php.bak",
+			splitPath: []string{".php"},
+			wantPos:   9,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotPos := Transport{SplitPath: tt.splitPath}.splitPos(tt.path)
+			assert.Equal(t, tt.wantPos, gotPos, "splitPos(%q, %v)", tt.path, tt.splitPath)
+
+			// Verify that the split produces valid substrings
+			if gotPos > 0 && gotPos <= len(tt.path) {
+				scriptName := tt.path[:gotPos]
+				pathInfo := tt.path[gotPos:]
+
+				// The script name should end with one of the split extensions (case-insensitive)
+				hasValidEnding := false
+				for _, split := range tt.splitPath {
+					if strings.HasSuffix(strings.ToLower(scriptName), split) {
+						hasValidEnding = true
+						break
+					}
+				}
+				assert.True(t, hasValidEnding, "script name %q should end with one of %v", scriptName, tt.splitPath)
+
+				// Original path should be reconstructable
+				assert.Equal(t, tt.path, scriptName+pathInfo, "path should be reconstructable from split parts")
+			}
+		})
+	}
+}
+
+// TestSplitPosUnicodeSecurityRegression specifically tests the vulnerability
+// described in GHSA-g966-83w7-6w38 where Unicode case-folding caused
+// incorrect SCRIPT_NAME/PATH_INFO splitting
+func TestSplitPosUnicodeSecurityRegression(t *testing.T) {
+	// U+023A: Ⱥ (UTF-8: C8 BA). Lowercase is ⱥ (UTF-8: E2 B1 A5), longer in bytes.
+	path := "/ȺȺȺȺshell.php.txt.php"
+	split := []string{".php"}
+
+	pos := Transport{SplitPath: split}.splitPos(path)
+
+	// The vulnerable code would return 22 (computed on lowercased string)
+	// The correct code should return 18 (position in original string)
+	expectedPos := strings.Index(path, ".php") + len(".php")
+	assert.Equal(t, expectedPos, pos, "split position should match first .php in original string")
+	assert.Equal(t, 18, pos, "split position should be 18, not 22")
+
+	if pos > 0 && pos <= len(path) {
+		scriptName := path[:pos]
+		pathInfo := path[pos:]
+
+		assert.Equal(t, "/ȺȺȺȺshell.php", scriptName, "script name should be the path up to first .php")
+		assert.Equal(t, ".txt.php", pathInfo, "path info should be the remainder after first .php")
+	}
+}