{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "aiosmtplib",
        "purl": "pkg:pypi/aiosmtplib"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.1.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.1",
        "0.1.2",
        "0.1.3",
        "0.1.4",
        "0.1.5rc2",
        "0.1.6",
        "0.1.7",
        "1.0.0",
        "1.0.1",
        "1.0.2",
        "1.0.3",
        "1.0.4",
        "1.0.5",
        "1.0.6",
        "1.1.0",
        "1.1.1",
        "1.1.2",
        "1.1.3",
        "1.1.4",
        "1.1.5",
        "1.1.6",
        "1.1.7",
        "1.1b0",
        "2.0.0",
        "2.0.0b0",
        "2.0.0b1",
        "2.0.1",
        "2.0.2",
        "3.0.0",
        "3.0.1",
        "3.0.2",
        "4.0.0",
        "4.0.1",
        "4.0.2",
        "5.0.0",
        "5.1.0"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-53533",
    "GHSA-v3q9-hj7j-63hq"
  ],
  "details": "### Summary\n\n`aiosmtplib`\u0027s `SMTP.mail()`, `SMTP.rcpt()`, `SMTP.vrfy()` and `SMTP.expn()` send the caller-supplied email address to the server without rejecting embedded CR/LF (`\\r\\n`) bytes. An address that contains a CR/LF is written verbatim onto the SMTP control connection, so the bytes after the CRLF are framed by the server as one or more **additional, standalone SMTP command lines**. A caller that passes an attacker-influenced sender or recipient address into `mail()`/`rcpt()` (or `vrfy()`/`expn()`) therefore allows **SMTP command injection** (CWE-93 / CWE-77): the attacker can smuggle arbitrary SMTP verbs such as `MAIL FROM`, `RCPT TO`, `RSET`, `DATA`, or `AUTH` into the session. Injected commands will cause the `SMTP` instance to hang, but all commands required to complete the envelope could be sent in one address string.\n\nThe `SMTP.sendmail()` command will pass sender and recipient addresses verbatim through to `SMTP.mail()` \u0026 `SMTP.rcpt()`, and so is also vulnerable. `SMTP.send_message()` is not affected.\n\n### Impact\n\nSeverity: medium. Type: SMTP protocol command injection (CWE-93 \u2014 Improper Neutralization of CRLF Sequences; CWE-77 \u2014 Command Injection).\n\nWhen an application built on `aiosmtplib` derives the envelope sender or any recipient from data an attacker can influence (a web form etc.) and passes it to `mail()`/`rcpt()` (directly, or via `sendmail()`/`send()` without a `Message` object), the attacker can:\n\n- desynchronize the command/response pipeline and cause the aiosmtplib client to hang, resulting in a possible denial of service\n- inject multiple commands in one address to send an arbitrary message\n\nThe address only needs to reach `mail()`/`rcpt()`/`vrfy()`/`expn()`; no attacker control over the SMTP server is required.\n\n### Vulnerable versions\n\nAffected version: `aiosmtplib` 5.1.0 (latest at time of report) and all earlier releases.\n\n### Credit\n\nReported by tonghuaroot.",
  "id": "PYSEC-2026-2338",
  "modified": "2026-07-13T16:03:20.193292Z",
  "published": "2026-07-13T15:46:29.471704Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/cole/aiosmtplib/security/advisories/GHSA-v3q9-hj7j-63hq"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/cole/aiosmtplib"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/aiosmtplib"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-v3q9-hj7j-63hq"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-53533"
    }
  ],
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:H/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "aiosmtplib vulnerable to SMTP command injection via CR/LF in sender/recipient address"
}