RCE in Ruby Net-Imap
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.
Vulnerability class: Command Injection (OS Command Injection)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.005 (42.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 43rd percentile — 42.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.005 · change: +0.001
Affected products
- Ruby Net-Imap — versions < 0.4.24, >= 0.5.0, < 0.5.14, >= 0.6.0, < 0.6.4
- Ruby-Lang Net\ — versions \
- Ruby-Lang Net\:\:imap
Weakness classification (CWE)
References
- github.com/ruby/net-imap/security/advisories/GHSA-hm49-wcqc-g2xg (Mitigation, Vendor Advisory)
- github.com/ruby/net-imap/releases/tag/v0.4.24 (Release Notes)
- github.com/ruby/net-imap/releases/tag/v0.5.14 (Release Notes)
- github.com/ruby/net-imap/releases/tag/v0.6.4 (Release Notes)
Frequently asked questions
- What is CVE-2026-42257?
- CVE-2026-42257 is a critical-severity vulnerability in Ruby Net-Imap, classified under Command Injection. CVSS score: 9.8/10. Published 2026-05-09.
- How severe is CVE-2026-42257?
- Critical severity. CVSS v3 base score is 9.8 out of 10.