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Net\Application · Ruby Lang

CVE-2026-42257

CRITICAL · 9.8 CVSS v3.1 Published 2026-05-09
Fix available
A fix is available. Upgrade to 0.4.24 / 0.5.14 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to versions 0.4.24, 0.5.14, and 0.6.4, several Net::IMAP commands accept a raw string argument that is sent to the server without validation or escaping. If this string is derived from user-controlled input, it may contain contain CRLF sequences, which an attacker can use to inject arbitrary IMAP commands. This issue has been patched in versions 0.4.24, 0.5.14, and 0.6.4.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Net::IMAP Ruby library versions prior to 0.4.24, 0.5.14, and 0.6.4 contain a CRLF injection vulnerability. Multiple IMAP commands accept raw string arguments that are sent to the server without validation or escaping, allowing attackers to inject arbitrary IMAP commands via CRLF sequences in user-controlled input.

MitigationUpgrade Net::IMAP to version 0.4.24, 0.5.14, or 0.6.4 or later. Additionally, validate and sanitize any user-controlled input before passing it to IMAP commands as a defense-in-depth measure.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Net\Application
Affected:< 0.4.24>= 0.5.0, < 0.5.14>= 0.6.0, < 0.6.4

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check Net::IMAP gem version
    Run `gem list net-imap` or add `puts Net::IMAP::VERSION` in Ruby code to see the installed version
    Affected if Version is < 0.4.24, OR >= 0.5.0 and < 0.5.14, OR >= 0.6.0 and < 0.6.4
  2. Inspect Gemfile or gemspec for Net::IMAP version constraint
    Look for `gem 'net-imap'` or `spec.add_runtime_dependency 'net-imap'` entries and compare the version requirement to the affected ranges
    Affected if The declared version falls within any of the affected ranges listed above
  3. Identify if application code passes user input to Net::IMAP commands
    Search codebase for Net::IMAP method calls like `login`, `authenticate`, `append`, `copy`, `move`, `store`, `select`, `examine`, `create`, `delete`, `rename`, `subscribe`, `unsubscribe`, `list`, `lsub`, `status`, or `idle` and trace whether external input (params, headers, body) flows into these calls
    Affected if User-controlled or external data is passed directly as arguments to any IMAP command without sanitization
  4. Check for custom IMAP command execution patterns
    Search for `send_command`, `raw`, or similar methods that construct IMAP commands dynamically, and verify if string interpolation or concatenation is used with unsanitized input
    Affected if The application builds custom IMAP commands using string concatenation with data that originates from external sources

You are affected if your installed Net::IMAP version is within the vulnerable ranges AND your application passes external input to IMAP command methods without validation.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 0.4.24 / 0.5.14 / 0.6.4 or later
Fixed in 0.4.240.5.140.6.4
Interim mitigation

Upgrade Net::IMAP to version 0.4.24, 0.5.14, or 0.6.4 or later. Additionally, validate and sanitize any user-controlled input before passing it to IMAP commands as a defense-in-depth measure.

Recommended fix High confidence

net-imap version 0.4.24, 0.5.14, or 0.6.4 depending on your current version branch; generally upgrade to the latest stable release that includes the fix

  1. Identify the current Net::IMAP version in your project by checking your Gemfile or gemspec file
  2. Determine which version branch you are currently on (0.4.x, 0.5.x, or 0.6.x)
  3. Run `bundle update net-imap` to update to the latest version in your current branch, or manually specify the fixed version
  4. If using RubyGems directly, run `gem install net-imap` to get the latest version
  5. Verify the installed version matches the fixed release (0.4.24, 0.5.14, or 0.6.4)
  6. Run your test suite to ensure compatibility
  7. Deploy the updated gem
Caveat Minimal risk - this is a security patch; however, test thoroughly as minor version bumps in the 0.6.x branch may include other changes

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Net\ Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,720
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-42257 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data