fix(secret): add UTF-8 validation in secret scanner to prevent protobuf marshalling errors (#9253)

Co-authored-by: knqyf263 <knqyf263@users.noreply.github.com>

pkg/fanal/secret/scanner.go

@@ -10,6 +10,7 @@ import (
 	"sort"
 	"strings"
 	"sync"
+	"unicode/utf8"
 
 	"github.com/samber/lo"
 	"golang.org/x/xerrors"
@@ -19,7 +20,12 @@ import (
 	"github.com/aquasecurity/trivy/pkg/log"
 )
 
-var lineSep = []byte{'\n'}
+var (
+	lineSep      = []byte{'\n'}
+	warnUTF8Once = sync.OnceFunc(func() {
+		log.WithPrefix(log.PrefixSecret).Warn("Invalid UTF-8 sequences detected in file content, replacing with empty string")
+	})
+)
 
 type Scanner struct {
 	logger *log.Logger
@@ -280,7 +286,7 @@ func ParseConfig(configPath string) (*Config, error) {
 		return nil, nil
 	}
 
-	logger := log.WithPrefix("secret").With("config_path", configPath)
+	logger := log.WithPrefix(log.PrefixSecret).With("config_path", configPath)
 	f, err := os.Open(configPath)
 	if errors.Is(err, os.ErrNotExist) {
 		// If the specified file doesn't exist, it just uses built-in rules and allow rules.
@@ -318,7 +324,7 @@ func convertSeverity(logger *log.Logger, severity string) string {
 }
 
 func NewScanner(config *Config) Scanner {
-	logger := log.WithPrefix("secret")
+	logger := log.WithPrefix(log.PrefixSecret)
 
 	// Use the default rules
 	if config == nil {
@@ -512,7 +518,7 @@ func findLocation(start, end int, content []byte) (int, int, types.Code, string)
 		lineStart = lo.Ternary(start-lineStart-30 < 0, lineStart, start-30)
 		lineEnd = lo.Ternary(end+20 > lineEnd, lineEnd, end+20)
 	}
-	matchLine := string(content[lineStart:lineEnd])
+	matchLine := sanitizeUTF8String(content[lineStart:lineEnd])
 	endLineNum := startLineNum + bytes.Count(content[start:end], lineSep)
 
 	var code types.Code
@@ -529,9 +535,9 @@ func findLocation(start, end int, content []byte) (int, int, types.Code, string)
 
 		var strRawLine string
 		if len(rawLine) > maxLineLength {
-			strRawLine = lo.Ternary(inCause, matchLine, string(rawLine[:maxLineLength]))
+			strRawLine = lo.Ternary(inCause, matchLine, sanitizeUTF8String(rawLine[:maxLineLength]))
 		} else {
-			strRawLine = string(rawLine)
+			strRawLine = sanitizeUTF8String(rawLine)
 		}
 
 		code.Lines = append(code.Lines, types.Line{
@@ -555,3 +561,14 @@ func findLocation(start, end int, content []byte) (int, int, types.Code, string)
 
 	return startLineNum + 1, endLineNum + 1, code, matchLine
 }
+
+// sanitizeUTF8String converts bytes to a valid UTF-8 string, logging a warning once if invalid sequences are found
+func sanitizeUTF8String(data []byte) string {
+	if utf8.Valid(data) {
+		return string(data)
+	}
+
+	warnUTF8Once()
+
+	return strings.ToValidUTF8(string(data), string(utf8.RuneError))
+}

pkg/fanal/secret/scanner_test.go

@@ -1406,6 +1406,42 @@ func TestSecretScanner(t *testing.T) {
 				Findings: []types.SecretFinding{wantFindingTokenInsideJs},
 			},
 		},
+		{
+			name:          "invalid UTF-8 sequences in secrets",
+			configPath:    filepath.Join("testdata", "skip-test.yaml"),
+			inputFilePath: filepath.Join("testdata", "invalid-utf8.txt"),
+			want: types.Secret{
+				FilePath: filepath.Join("testdata", "invalid-utf8.txt"),
+				Findings: []types.SecretFinding{
+					{
+						RuleID:    "github-pat",
+						Category:  secret.CategoryGitHub,
+						Title:     "GitHub Personal Access Token",
+						Severity:  "CRITICAL",
+						StartLine: 1,
+						EndLine:   1,
+						Match:     "token=****************************************",
+						Code: types.Code{
+							Lines: []types.Line{
+								{
+									Number:      1,
+									Content:     "token=****************************************",
+									Highlighted: "token=****************************************",
+									IsCause:     true,
+									FirstCause:  true,
+									LastCause:   true,
+								},
+								{
+									Number:      2,
+									Content:     "# Comment with invalid UTF-8: <20>",
+									Highlighted: "# Comment with invalid UTF-8: <20>",
+								},
+							},
+						},
+					},
+				},
+			},
+		},
 	}
 
 	for _, tt := range tests {

pkg/fanal/secret/testdata/invalid-utf8.txt

@@ -0,0 +1,3 @@
+token=ghp_abcdef1234567890ABCDEF1234567890abcd
+# Comment with invalid UTF-8: <20><><EFBFBD><EFBFBD>
+token2=ghp_1234567890abcdef1234567890ABCDEF<45><46>abcd