CVE-2026-53533: Aiosmtplib Aiosmtplib Vulnerable To SMTP Command Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-v3q9-hj7j-63hq",
  "modified" : "2026-07-07T23:40:52Z",
  "published" : "2026-07-07T23:40:52Z",
  "aliases" : [ "CVE-2026-53533" ],
  "summary" : "aiosmtplib vulnerable to SMTP command injection via CR/LF in sender/recipient address",
  "details" : "### Summary\n\n`aiosmtplib`'s `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()` & `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 — Improper Neutralization of CRLF Sequences; CWE-77 — 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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "aiosmtplib"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "5.1.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 5.1.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/cole/aiosmtplib/security/advisories/GHSA-v3q9-hj7j-63hq"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/cole/aiosmtplib"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-77", "CWE-93" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-07T23:40:52Z",
    "nvd_published_at" : null
  }
}