Update dependency net-imap to v0.5.7 [SECURITY]

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
net-imap (changelog)	0.5.6 -> 0.5.7

GitHub Vulnerability Alerts

CVE-2025-43857

Summary

There is a possibility for denial of service by memory exhaustion when net-imap reads server responses. At any time while the client is connected, a malicious server can send can send a "literal" byte count, which is automatically read by the client's receiver thread. The response reader immediately allocates memory for the number of bytes indicated by the server response.

This should not be an issue when securely connecting to trusted IMAP servers that are well-behaved. It can affect insecure connections and buggy, untrusted, or compromised servers (for example, connecting to a user supplied hostname).

Details

The IMAP protocol allows "literal" strings to be sent in responses, prefixed with their size in curly braces (e.g. {1234567890}\r\n). When Net::IMAP receives a response containing a literal string, it calls IO#read with that size. When called with a size, IO#read immediately allocates memory to buffer the entire string before processing continues. The server does not need to send any more data. There is no limit on the size of literals that will be accepted.

Fix

Upgrade

Users should upgrade to net-imap 0.5.7 or later. A configurable max_response_size limit has been added to Net::IMAP's response reader. The max_response_size limit has also been backported to net-imap 0.2.5, 0.3.9, and 0.4.20.

To set a global value for max_response_size, users must upgrade to net-imap ~> 0.4.20, or > 0.5.7.

Configuration

To avoid backward compatibility issues for secure connections to trusted well-behaved servers, the default max_response_size for net-imap 0.5.7 is very high (512MiB), and the default max_response_size for net-imap ~> 0.4.20, ~> 0.3.9, and 0.2.5 is nil (unlimited).

When connecting to untrusted servers or using insecure connections, a much lower max_response_size should be used.

# Set the global max_response_size (only ~> v0.4.20, > 0.5.7)
Net::IMAP.config.max_response_size = 256 << 10 # 256 KiB

# Set when creating the connection
imap = Net::IMAP.new(hostname, ssl: true,
                     max_response_size: 16 << 10) # 16 KiB

# Set after creating the connection
imap.max_response_size = 256 << 20 # 256 KiB

# flush currently waiting read, to ensure the new setting is loaded
imap.noop

Please Note: max_response_size only limits the size per response. It does not prevent a flood of individual responses and it does not limit how many unhandled responses may be stored on the responses hash. Users are responsible for adding response handlers to prune excessive unhandled responses.

Compatibility with lower max_response_size

A lower max_response_size may cause a few commands which legitimately return very large responses to raise an exception and close the connection. The max_response_size could be temporarily set to a higher value, but paginated or limited versions of commands should be used whenever possible. For example, to fetch message bodies:

imap.max_response_size = 256 << 20 # 256 KiB
imap.noop # flush currently waiting read

# fetch a message in 252KiB chunks
size = imap.uid_fetch(uid, "RFC822.SIZE").first.rfc822_size
limit = 252 << 10
message = ((0..size) % limit).each_with_object("") {|offset, str|
  str << imap.uid_fetch(uid, "BODY.PEEK[]<#{offset}.#{limit}>").first.message(offset:)
}

imap.max_response_size = 16 << 20 # 16 KiB
imap.noop # flush currently waiting read

References

• PR to introduce max_response_size: https://github.com/ruby/net-imap/pull/444
  • Specific commit: 0ae8576c1 - lib/net/imap/response_reader.rb
• Backport to 0.4: https://github.com/ruby/net-imap/pull/445
• Backport to 0.3: https://github.com/ruby/net-imap/pull/446
• Backport to 0.2: https://github.com/ruby/net-imap/pull/447

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Release Notes

ruby/net-imap (net-imap)

v0.5.7

Compare Source

What's Changed

🔒 Security

This release adds two features to prevent unbounded memory use: the response_handlers keyword argument to Net::IMAP.new (https://github.com/ruby/net-imap/pull/419) so response handlers can be added before the server can send any responses, and the max_response_size config attribute (https://github.com/ruby/net-imap/pull/444, GHSA-j3g3-5qv5-52mj, CVE-2025-43857, reported by @​Masamuneee).

[!NOTE]
The default max_response_size is extremely high, to avoid issues with secure connections to trusted servers that are well-behaved. It can be configured more conservatively to guard against untrusted servers (for example, connecting to user-provided hostnames). It is the responsibility of net-imap users to configure their client appropriately for the server they are connecting to.

Added

• ✨ Track IMAP connection state by @​nevans in https://github.com/ruby/net-imap/pull/416
• ✨ Add response_handlers kwarg to Net::IMAP.new by @​nevans in https://github.com/ruby/net-imap/pull/419
• ✨ Customize SequenceSet YAML serialization by @​nevans in https://github.com/ruby/net-imap/pull/432
• ✨ Limit max_response_size by @​nevans in https://github.com/ruby/net-imap/pull/444

Documentation

• 📚 Improve docs for unbounded memory use and thread safety by @​nevans in https://github.com/ruby/net-imap/pull/418
• 📚 Impove SequenceSet docs by @​nevans in https://github.com/ruby/net-imap/pull/420
• 📚 Doc improvements for open_timeout, etc by @​nevans in https://github.com/ruby/net-imap/pull/424

Other Changes

• ♻️ Reorganize Config.version_defaults creation by @​nevans in https://github.com/ruby/net-imap/pull/412
• ♻️ Refactor Config attr type coercion by @​nevans in https://github.com/ruby/net-imap/pull/417
• ♻️ Refactor Net::IMAP#get_response (internal) by @​nevans in https://github.com/ruby/net-imap/pull/422
• ♻️ Rational config versions by @​nevans in https://github.com/ruby/net-imap/pull/429
• ♻️ Extract ResponseReader from get_response by @​nevans in https://github.com/ruby/net-imap/pull/433
• ♻️ Refactor ResponseReader by @​nevans in https://github.com/ruby/net-imap/pull/435

Miscellaneous

• Bump step-security/harden-runner from 2.10.4 to 2.11.0 by @​dependabot in https://github.com/ruby/net-imap/pull/409
• ✅ Make FakeServer more robust against disconnect by @​nevans in https://github.com/ruby/net-imap/pull/414
• ✅ Improvements to FakeServer (tests only) by @​nevans in https://github.com/ruby/net-imap/pull/415
• ✅ Ignore more IO errors in some FakeServer tests by @​nevans in https://github.com/ruby/net-imap/pull/421
• ⬆️ Bump step-security/harden-runner from 2.11.0 to 2.11.1 by @​dependabot in https://github.com/ruby/net-imap/pull/423

Full Changelog: ruby/net-imap@v0.5.6...v0.5.7

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[coveralls]

coverage: 99.07%. remained the same
when pulling 98855de on renovate/rubygems-net-imap-vulnerability
into 3425143 on main.