CVE-2021-41270 (PHP, published 2021-11-24T19:15Z)
Description: value: Symfony/Serializer handles serializing and deserializing data structures for Symfony, a PHP framework for web and console applications and a set of reusable PHP components. Symfony versions 4.1.0 before 4.4.35 and versions 5.0.0 before 5.3.12 are vulnerable to CSV injection, also known as formula injection. In Symfony 4.1, maintainers added the opt-in `csv_escape_formulas` option in the `CsvEncoder`, to prefix all cells starting with `=`, `+`, `-` or `@` with a tab `\t`. Since then, OWASP added 2 chars in that list: Tab (0x09) and Carriage return (0x0D). This makes the previous prefix char (Tab `\t`) part of the vulnerable characters, and OWASP suggests using the single quote `'` for prefixing the value. Starting with versions 4.4.34 and 5.3.12, Symfony now follows the OWASP recommendations and uses the single quote `'` to prefix formulas and add the prefix to cells starting by `\t`, `\r` as well as `=`, `+`, `-` and `@`.
Severity: MEDIUM (CVSS v3 base score: 6.5)
Weakness: CWE-1236 \u2014 Improper Neutralization of Formula Elements in a CSV File
The product saves user-provided information into a Comma-Separated Value (CSV) file, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as a command when the file is opened by a spreadsheet product.
Repository: https://github.com/symfony/symfony
Files changed:
src/Symfony/Component/Serializer/Encoder/CsvEncoder.php
src/Symfony/Component/Serializer/Tests/Encoder/CsvEncoderTest.php
Commit message: Use single quote to escape formulas


Vulnerable code:
    private $formulasStartCharacters = ['=', '-', '+', '@'];
                if ($escapeFormulas && \in_array(substr((string) $value, 0, 1), $this->formulasStartCharacters, true)) {
                    $result[$parentKey.$key] = "\t".$value;
"	=2+3"
"	-2+3"
"	+2+3"
"	@MyDataColumn"
"	=2+3"
"	-2+3"
"	+2+3"
"	@MyDataColumn"

Fixed code:
    private const FORMULAS_START_CHARACTERS = ['=', '-', '+', '@', "\t", "\r"];

                if ($escapeFormulas && \in_array(substr((string) $value, 0, 1), self::FORMULAS_START_CHARACTERS, true)) {
                    $result[$parentKey.$key] = "'".$value;
'=2+3
'-2+3
'+2+3
'@MyDataColumn

        $this->assertSame(<<<'CSV'
0
"'	tab"

CSV
            , $this->encoder->encode(["\ttab"], 'csv'));

        $this->assertSame(<<<'CSV'
0
"'=1+2"";=1+2"

CSV
            , $this->encoder->encode(['=1+2";=1+2'], 'csv'));

        $this->assertSame(<<<'CSV'
0
"'=1+2'"" ;,=1+2"

CSV
            , $this->encoder->encode(['=1+2\'" ;,=1+2'], 'csv'));

        $this->assertSame(<<<'CSV'
0
"	tab"

CSV
            , $this->encoder->encode(["\ttab"], 'csv'));

        $this->assertSame(<<<'CSV'
0
"=1+2"";=1+2"

CSV
            , $this->encoder->encode(['=1+2";=1+2'], 'csv'));

        $this->assertSame(<<<'CSV'
0
"=1+2'"" ;,=1+2"

CSV
            , $this->encoder->encode(['=1+2\'" ;,=1+2'], 'csv'));
'=2+3
'-2+3
'+2+3
'@MyDataColumn

        $this->assertSame(<<<'CSV'
0
"'	tab"

CSV
            , $this->encoder->encode(["\ttab"], 'csv', [
                CsvEncoder::ESCAPE_FORMULAS_KEY => true,
            ]));

        $this->assertSame(<<<'CSV'
0
"'=1+2"";=1+2"

CSV
            , $this->encoder->encode(['=1+2";=1+2'], 'csv', [
                CsvEncoder::ESCAPE_FORMULAS_KEY => true,
            ]));

        $this->assertSame(<<<'CSV'
0
"'=1+2'"" ;,=1+2"

CSV
            , $this->encoder->encode(['=1+2\'" ;,=1+2'], 'csv', [
                CsvEncoder::ESCAPE_FORMULAS_KEY => true,
            ]));