CVE-2026-42257
CVE-2026-42257 is a critical-severity vulnerability in Ruby-lang Net with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-77.
Key facts
- Severity: Critical (CVSS 3.x base score 9.8)
- CVSS v4: 5.8
- EPSS exploit prediction: 0% (35th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-28926
- Weakness: CWE-77
- Affected product: Ruby-lang Net
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2026-42257?
- 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.
- How severe is CVE-2026-42257?
- CVE-2026-42257 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
- Is CVE-2026-42257 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-42257?
- CVE-2026-42257 affects Ruby-lang Net. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-42257?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
- Does CVE-2026-42257 have an EU (EUVD) identifier?
- Yes. CVE-2026-42257 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-28926.
- When was CVE-2026-42257 published?
- CVE-2026-42257 was published on 2026-05-09 and last updated on 2026-06-17.
References
- https://github.com/ruby/net-imap/releases/tag/v0.4.24
- https://github.com/ruby/net-imap/releases/tag/v0.5.14
- https://github.com/ruby/net-imap/releases/tag/v0.6.4
- https://github.com/ruby/net-imap/security/advisories/GHSA-hm49-wcqc-g2xg
Affected products (1)
- cpe:2.3:a:ruby-lang:net\:\:imap:*:*:*:*:*:ruby:*:*
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