CVE-2026-47240: Net :IMAP: Command Injection Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-8p34-64r3-mwg8",
  "modified" : "2026-07-06T22:53:42Z",
  "published" : "2026-06-09T18:36:04Z",
  "aliases" : [ "CVE-2026-47240" ],
  "summary" : "Net::IMAP: Command Injection via non-synchronizing literal in \"raw\" argument",
  "details" : "Several Net::IMAP commands accept a \"raw data\" argument that is sent verbatim after validation to prevent command injection.  However, if a server does not support non-synchronizing literals, it may still be possible to inject arbitrary IMAP commands inside non-synchronizing literals.\n\n### Details\n\nRaw data arguments support embedded literal values, both synchronizing and non-synchronizing.  Non-synchronizing literals can only be safely sent when the server advertises any of the `LITERAL+`, `LITERAL-`, or `IMAP4rev2` capabilities.  But raw data arguments do not verify server support for non-synchronizing literals prior to sending.\n\nServers without support for non-synchronizing literals could handle them in several different ways:  If a server sees a `\"}\\r\\n\"` byte sequence but can't parse the literal bytesize, it _may_ cautiously decide to close the connection, blocking any command injection attacks.  However, a server without support for non-synchronizing literals may instead interpret the `\"+}\\r\\n\"` as the end of a malformed command line and respond with a tagged `BAD`.  In that case, the contents of the literal will be interpreted as one or more new pipelined commands, allowing a CRLF command injection attack to succeed.\n\nThis affects the following commands' string arguments:\n* `criteria` for `#search` and `#uid_search`\n* `search_keys` for `#sort`, `#thread`, `#uid_sort`, and `#uid_thread`\n* `attr` for `#fetch` and `#uid_fetch`\n\nPrior to `net-imap` v0.6.4, v0.5.14, and v0.4.24, raw data arguments were not validated in _any_ way, so they were also vulnerable to this attack.  See CVE-2026-42257 (GHSA-hm49-wcqc-g2xg).\n\n### Impact\n\nFortunately, `LITERAL-` is supported by most modern IMAP servers.  Even without support for non-synchronizing literals, cautious servers may handle invalid literal bytesize by closing the connection .  However, servers which handle a non-synchronizing literal just like any other malformed command will enable this vulnerability.\n\nIf a developer passes an unvalidated user-controlled input for one of these method arguments, an attacker can append CRLF sequence followed by a new IMAP command (like DELETE mailbox). Although this does not directly enable data exfiltration, it could be combined with other attack vectors or knowledge of the target system's attributes, e.g.: shared mail folders or the application's installed response handlers.\n\n### Mitigation\n\nUpdate to a version of `net-imap` which validates server support for non-synchronizing literals before sending them.\n\nIf upgrading `net-imap` is not possible:\n* Explicitly validate user-controlled inputs to prevent embedded non-synchronizing literals unless the server supports them.\n* For a simpler, more cautious approach: all embedded literals can be unconditionally prohibited, by checking that string inputs do not contain any CR or LF bytes.\n* Verify that the server advertises any of the `LITERAL+`, `LITERAL-`, or `IMAP4rev2` capabilities before using untrusted string inputs for the affected \"raw data\" arguments.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "net-imap"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.6.0"
      }, {
        "fixed" : "0.6.4.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.6.4"
    }
  }, {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "net-imap"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.5.15"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.5.14"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/ruby/net-imap/security/advisories/GHSA-8p34-64r3-mwg8"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-47240"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/ruby/net-imap"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ruby/net-imap/releases/tag/v0.6.4.1"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/net-imap/CVE-2026-47240.yml"
  }, {
    "type" : "WEB",
    "url" : "https://www.cve.org/CVERecord?id=CVE-2026-47240"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-77", "CWE-93" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-09T18:36:04Z",
    "nvd_published_at" : "2026-06-22T21:16:24Z"
  }
}