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CVE-2026-42257

Ruby-lang Net::imap command injection

9.8 CRITICALEPSS 0.52%
  1. Published9 May 2026

Description

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Ruby-lang Net::imap≥ 0.5.0 < 0.5.14 · ≥ 0.6.0 < 0.6.4 · < 0.4.24

Remediation

Fixed in
Ruby-lang Net::imap≥ 0.5.14

References

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Frequently asked

Is CVE-2026-42257 being actively exploited?

CVE-2026-42257 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.52%.

How severe is CVE-2026-42257?

CVE-2026-42257 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.52% probability of exploitation.

Which products are affected by CVE-2026-42257?

Affected products include Ruby-lang Net::imap.

How do I fix CVE-2026-42257?

Upgrade affected software to a fixed version, for example Ruby-lang Net::imap 0.5.14 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-42257 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.