[MM-30344] utils/markdown: fix index out of range (#16250)

* utils/markdown: fix index out of range

* reflect review comments

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

utils/markdown/links.go

@@ -147,7 +147,7 @@ func parseImageDimensions(markdown string, position int) (raw Range, next int, o
 
 	// Read width
 	hasWidth := false
-	for isNumericByte(markdown[position]) {
+	for position < len(markdown)-1 && isNumericByte(markdown[position]) {
 		hasWidth = true
 		position += 1
 	}
@@ -158,14 +158,14 @@ func parseImageDimensions(markdown string, position int) (raw Range, next int, o
 	}
 
 	// Read the x
-	if markdown[position] != 'x' && markdown[position] != 'X' {
+	if (markdown[position] != 'x' && markdown[position] != 'X') || position == len(markdown)-1 {
 		return
 	}
 	position += 1
 
 	// Read height
 	hasHeight := false
-	for isNumericByte(markdown[position]) {
+	for position < len(markdown)-1 && isNumericByte(markdown[position]) {
 		hasHeight = true
 		position += 1
 	}

utils/markdown/links_test.go

@@ -136,6 +136,27 @@ func TestParseImageDimensions(t *testing.T) {
 			ExpectedNext:  0,
 			ExpectedOk:    false,
 		},
+		"garbage 5": {
+			Input:         `![alt](https://example.com =100x200`,
+			Position:      27,
+			ExpectedRange: Range{0, 0},
+			ExpectedNext:  0,
+			ExpectedOk:    false,
+		},
+		"garbage 6": {
+			Input:         `![alt](https://example.com =100x`,
+			Position:      27,
+			ExpectedRange: Range{0, 0},
+			ExpectedNext:  0,
+			ExpectedOk:    false,
+		},
+		"garbage 7": {
+			Input:         `![alt](https://example.com =x200`,
+			Position:      27,
+			ExpectedRange: Range{0, 0},
+			ExpectedNext:  0,
+			ExpectedOk:    false,
+		},
 	} {
 		t.Run(name, func(t *testing.T) {
 			raw, next, ok := parseImageDimensions(tc.Input, tc.Position)