diff --git a/lib/classes/dataformat.php b/lib/classes/dataformat.php
index 70bdcec5a6b..ba33494989c 100644
--- a/lib/classes/dataformat.php
+++ b/lib/classes/dataformat.php
@@ -167,4 +167,44 @@ class dataformat {
 
         return get_file_storage()->create_file_from_pathname($filerecord, $filepath);
     }
+
+    /**
+     * Escape formula spreadsheet values.
+     *
+     * Check values being used in spreadsheets and make them safe for inclusion.
+     * Following OWASP recommendations {@link https://owasp.org/www-community/attacks/CSV_Injection}.
+     *
+     * @param string|null $value Value to check.
+     * @return string|null Return escaped formula if detected.
+     */
+    public static function escape_spreadsheet_formula($value): ?string {
+        // Only escape strings; leave numbers and other types unchanged.
+        if (!is_string($value)) {
+            return $value;
+        }
+
+        // Moodle's null placeholder: exactly one dash.
+        if ($value === '-') {
+            return $value;
+        }
+
+        // Trim only for checking, not for modifying output.
+        $trimmed = ltrim($value);
+
+        if ($trimmed === '') {
+            return $value;
+        }
+
+        // Characters that trigger formula parsing in Excel/Sheets.
+        $formulacharacters = ['=', '+', '-', '@'];
+
+        // If trimmed version starts with formula character, escape it.
+        if (in_array($trimmed[0], $formulacharacters, true)) {
+            // Preserve original whitespace. Do not alter actual content.
+            return "'" . $value;
+        }
+
+        return $value;
+    }
+
 }
diff --git a/lib/classes/dataformat/spout_base.php b/lib/classes/dataformat/spout_base.php
index 4c582707ec3..ead5b879d61 100644
--- a/lib/classes/dataformat/spout_base.php
+++ b/lib/classes/dataformat/spout_base.php
@@ -120,7 +120,11 @@ abstract class spout_base extends \core\dataformat\base {
      * @param int $rownum
      */
     public function write_record($record, $rownum) {
-        $row = \Box\Spout\Writer\Common\Creator\WriterEntityFactory::createRowFromArray($this->format_record($record));
+        $rowvalues = $this->format_record($record);
+        foreach ($rowvalues as $key => $value) {
+            $rowvalues[$key] = \core\dataformat::escape_spreadsheet_formula($value);
+        }
+        $row = \Box\Spout\Writer\Common\Creator\WriterEntityFactory::createRowFromArray($rowvalues);
         $this->writer->addRow($row);
     }
 
diff --git a/lib/tests/dataformat_test.php b/lib/tests/dataformat_test.php
index ebd10b0910a..f48997ebeec 100644
--- a/lib/tests/dataformat_test.php
+++ b/lib/tests/dataformat_test.php
@@ -112,4 +112,80 @@ class dataformat_test extends \advanced_testcase {
         $this->assertStringStartsWith($filerecord['filename'], $file->get_filename());
         $this->assertGreaterThan(0, $file->get_filesize());
     }
+
+    /**
+     * Data provider for test_escape_spreadsheet_formula.
+     *
+     * @return array
+     */
+    public static function escape_spreadsheet_formula_provider(): array {
+        return [
+            'null stays null' => [
+                null,
+                null,
+            ],
+            'empty string stays empty' => [
+                '',
+                '',
+            ],
+            'Formula with tab' => [
+                'value' => "\t=SUM(1+1)",
+                'expected' => "'\t=SUM(1+1)",
+            ],
+            'Formula with carriage return' => [
+                'value' => "\r=SUM(1+1)",
+                'expected' => "'\r=SUM(1+1)",
+            ],
+            'Formula with new line' => [
+                'value' => "\n=SUM(1+1)",
+                'expected' => "'\n=SUM(1+1)",
+            ],
+            'Formula starting with "="' => [
+                'value' => "=SUM(1+1)",
+                'expected' => "'=SUM(1+1)",
+            ],
+            'Formula starting with "+"' => [
+                'value' => "+1+1",
+                'expected' => "'+1+1",
+            ],
+            'Formula starting with "-"' => [
+                'value' => "-1+1",
+                'expected' => "'-1+1",
+            ],
+            'Formula starting with "@"' => [
+                'value' => "@A5",
+                'expected' => "'@A5",
+            ],
+            'Null placeholder' => [
+                'value' => "-",
+                'expected' => "-",
+            ],
+            'dash with leading space is not placeholder, so escaped' => [
+                ' -',
+                "' -",
+            ],
+            'dash with trailing space is not placeholder, so escaped' => [
+                '- ',
+                "'- ",
+            ],
+            'Non-formula' => [
+                'value' => "Hello there",
+                'expected' => "Hello there",
+            ],
+        ];
+    }
+
+    /**
+     * Test escape_spreadsheet_formula.
+     *
+     * @dataProvider escape_spreadsheet_formula_provider
+     * @param string|null $value The value to test.
+     * @param string|null $expected The expected value after escaping.
+     */
+    public function test_escape_spreadsheet_formula(?string $value, ?string $expected): void {
+        $this->resetAfterTest();
+
+        $escapedvalue = dataformat::escape_spreadsheet_formula($value);
+        $this->assertEquals($expected, $escapedvalue);
+    }
 }
diff --git a/lib/tests/tablelib_test.php b/lib/tests/tablelib_test.php
index 7f3676434d9..c41bcaf9b44 100644
--- a/lib/tests/tablelib_test.php
+++ b/lib/tests/tablelib_test.php
@@ -829,4 +829,33 @@ final class tablelib_test extends \advanced_testcase {
         $this->expectOutputRegex('/' . '<caption class="inline">' . $caption . '<\/caption>' . '/');
     }
 
+    /**
+     * Test formulas are escaped in exported tables.
+     */
+    public function test_table_exports_escaped_formulas(): void {
+        $table = new flexible_table('tablelib_test_export');
+        $table->define_baseurl('/invalid.php');
+        $table->define_columns(['c1', 'c2', 'c3', 'c4', 'c5', 'c6', 'c7', 'c8']);
+
+        ob_start();
+        $table->is_downloadable(true);
+        $table->is_downloading('csv');
+
+        $table->setup();
+        $table->add_data([
+            'column0' => "\t=SUM(1+1)", // With tab.
+            'column1' => "\r=SUM(1+1)", // With carriage return.
+            'column2' => "\n=SUM(1+1)", // With new line.
+            'column3' => "=SUM(1+1)",
+            'column4' => "=1+1",
+            'column5' => "+1+1",
+            'column6' => "-1+1",
+            'column7' => "@A1",
+            'column8' => "-", // Single dash (should not be escaped).
+        ]);
+        $output = ob_get_contents();
+        ob_end_clean();
+
+        $this->assertEquals("\n'=SUM(1+1),'=SUM(1+1),'=SUM(1+1),'=SUM(1+1),'=1+1,'+1+1,'-1+1,'@A1,-\n", substr($output, 3));
+    }
 }