Is CVE-2026-42257 in the CISA KEV catalog?

No. CVE-2026-42257 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-42257?

CVE-2026-42257 has a CVSS v3 base score of 9.8 (Moderate).

What is the EPSS score for CVE-2026-42257?

CVE-2026-42257 has an EPSS score of 0.43% (34th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-42257?

Upgrade libruby2.3 on ubuntu 16.04 to 2.3.1-2~ubuntu16.04.16+esm14 or later. Fixes are available for 4 affected products.

CVE & CISA-KEV Catalog

CVE-2026-42257

MEDIUM

9.8

CVSS v3

NVD

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.

CWE-77Command Injection CWE-93

How to fix

Remediation Available

libruby2.3Ubuntu

Fixed in:2.3.1-2~ubuntu16.04.16+esm14USN-8431-1

libruby2.5Ubuntu

Fixed in:2.5.1-1ubuntu1.16+esm8USN-8431-1

ruby2.3Ubuntu

Fixed in:2.3.1-2~ubuntu16.04.16+esm14USN-8431-1

ruby2.5Ubuntu

Fixed in:2.5.1-1ubuntu1.16+esm8USN-8431-1

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

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

Exploit Intelligence

0.43%probability of exploitation in 30 days

34thpercentile

Low risk: more likely to be exploited than 34% of all known CVEs.

References

Vendor Advisory1

github.com

Release Notes3

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-05-18.