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Fencer Vulns
critical 9.8

CVE-2026-42257 json

net-imap: Command Injection via "raw" arguments to multiple commands

published 2026-05-04 6 mo ago modified 2026-09-10 1 mo ago also EUVD-2026-28926 , GHSA-hm49-wcqc-g2xg

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 37%
public exploits
0
none known

Summary

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.

Patch / fix

  • rubygems net-imap 0.4.24, 0.5.14, 0.6.4
  • ruby-lang net-imap 0.4.24, 0.5.14, 0.6.4
  • ruby-lang net::imap 0.4.24, 0.5.14, 0.6.4
  • ruby3.3 Debian 13 3.3.13-0+deb13u1

debian advisories DEBIAN-CVE-2026-42257

  • ruby3.0 Ubuntu 22.04 LTS 3.0.2-7ubuntu2.13
  • ruby3.2 Ubuntu 24.04 LTS 3.2.3-1ubuntu0.24.04.8
  • ruby3.3 Ubuntu 26.04 LTS 3.3.8-2ubuntu3.1
  • ruby2.3 Ubuntu Pro 16.04 LTS 2.3.1-2~ubuntu16.04.16+esm14
  • ruby2.5 Ubuntu Pro 18.04 LTS 2.5.1-1ubuntu1.16+esm8
  • ruby2.7 Ubuntu Pro 20.04 LTS 2.7.0-5ubuntu1.18+esm5

ubuntu advisories UBUNTU-CVE-2026-42257

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • ruby RHEL 9 3.3.12-8.module+el9.8.0+24568+2bbebe96
  • rubygems RHEL 9 3.5.22-8.module+el9.8.0+24568+2bbebe96
  • ruby-libs RHEL 9 3.3.12-8.module+el9.8.0+24568+2bbebe96
  • rubygem-pg RHEL 9 1.5.4-2.module+el9.8.0+24356+77305e91
  • rubygem-irb RHEL 9 1.13.1-8.module+el9.8.0+24568+2bbebe96
  • rubygem-rbs RHEL 9 3.4.0-8.module+el9.8.0+24568+2bbebe96
  • rubygem-rss RHEL 9 0.3.1-8.module+el9.8.0+24568+2bbebe96
  • rubygem-json RHEL 9 2.7.2-8.module+el9.8.0+24568+2bbebe96

red hat advisories RHSA-2026:50828RHSA-2026:50827RHSA-2026:50778RHSA-2026:50773RHSA-2026:50728RHSA-2026:40380

  • ruby AlmaLinux 8 3.3.12-8.module_el8.10.0+4241+4264e34b
  • rubygems AlmaLinux 8 3.5.22-8.module_el8.10.0+4241+4264e34b
  • ruby-libs AlmaLinux 8 3.3.12-8.module_el8.10.0+4241+4264e34b
  • rubygem-pg AlmaLinux 8 1.5.4-1.module_el8.10.0+3799+191214cc
  • rubygem-irb AlmaLinux 8 1.13.1-8.module_el8.10.0+4241+4264e34b
  • rubygem-rbs AlmaLinux 8 3.4.0-8.module_el8.10.0+4241+4264e34b
  • rubygem-rss AlmaLinux 8 0.3.1-8.module_el8.10.0+4241+4264e34b
  • rubygem-abrt AlmaLinux 8 0.4.0-1.module_el8.10.0+3799+191214cc

almalinux advisories ALSA-2026:50728ALSA-2026:50773ALSA-2026:50778ALSA-2026:50827ALSA-2026:50828

  • ruby4.0 Rocky Linux 10 4.0.6-36.el10_2
  • ruby Rocky Linux 10 3.3.12-14.el10_2
  • ruby Rocky Linux 9 4.0.6-34.module+el9.8.0+40271+b5850c84
  • rubygem-pg Rocky Linux 9 1.6.3-1.module+el9.8.0+40094+ce01217c
  • rubygem-mysql2 Rocky Linux 9 0.5.7-1.module+el9.8.0+40094+ce01217c
  • ruby Rocky Linux 9 3.3.12-8.module+el9.8.0+40270+7a73441e
  • rubygem-pg Rocky Linux 9 1.5.4-2.module+el9.7.0+40188+314ad260.0.1
  • rubygem-mysql2 Rocky Linux 9 0.5.5-3.module+el9.7.0+40032+36e56d0d

rocky linux advisories RLSA-2026:50773RLSA-2026:50778RLSA-2026:50827RLSA-2026:50828RLSA-2026:50728

  • ruby-net-imap Alpine 3.21 0.4.25-r0

alpine advisories ALPINE-CVE-2026-42257

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-42257 updated cvss 6.1

net-imap: Net::IMAP: Arbitrary IMAP command injection via CRLF sequences in unvalidated input

  • Red Hat 3scale API Management Platform 2 3scale-amp21/zync, 3scale-amp22/zync, 3scale-amp21/system, 3scale-amp22/system, 3scale-amp2/zync-rhel8, 3scale-amp2/zync-rhel9, +3 more
    affected: no fix available, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 8) ruby 3.3.12-8.module+el8.10.0+24567+c4e5368e, rubygems 3.5.22-8.module+el8.10.0+24567+c4e5368e, ruby-libs 3.3.12-8.module+el8.10.0+24567+c4e5368e, rubygem-pg 1.5.4-1.module+el8.10.0+21226+b78a28c4, rubygem-rbs 3.4.0-8.module+el8.10.0+24567+c4e5368e, rubygem-rss 0.3.1-8.module+el8.10.0+24567+c4e5368e, +18 more
    fixed: vendor fix RHSA-2026:50728
  • Red Hat Enterprise Linux AppStream (v. 9) ruby 3.3.12-8.module+el9.8.0+24568+2bbebe96, ruby 4.0.6-34.module+el9.8.0+24564+e55418dc, rubygems 3.5.22-8.module+el9.8.0+24568+2bbebe96, ruby-libs 3.3.12-8.module+el9.8.0+24568+2bbebe96, ruby-libs 4.0.6-34.module+el9.8.0+24564+e55418dc, rubygem-pg 1.5.4-2.module+el9.8.0+24356+77305e91, +40 more
    fixed: vendor fix RHSA-2026:50828
  • Red Hat Enterprise Linux AppStream (v. 10) ruby 3.3.12-14.el10_2, ruby4.0 4.0.6-36.el10_2, rubygems 3.5.22-14.el10_2, ruby-libs 3.3.12-14.el10_2, rubygem-rbs 3.4.0-14.el10_2, rubygem-rss 0.3.1-14.el10_2, +18 more Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) ruby-doc 3.3.12-14.el10_2, ruby4.0-doc 4.0.6-36.el10_2
    fixed: vendor fix RHSA-2026:50778
  • Red Hat Hardened Images ruby4.0 4.0.5-35.hum1, ruby3.4 3.4.10-31.hum1, ruby3.3 3.3.10-23.4.hum1, ruby4.0-libs 4.0.5-35.hum1, ruby3.4-libs 3.4.10-31.hum1, ruby3.3-libs 3.3.10-23.4.hum1, +6 more
    fixed: vendor fix RHSA-2026:40380
  • Red Hat Hardened Images rubygem3.4-rbs 3.8.0-31.hum1, rubygem3.4-rss 0.3.1-31.hum1, rubygem4.0-rss 0.3.2-35.hum1, rubygem3.4-irb 1.14.3-31.hum1, rubygem3.4-json 2.9.1-31.hum1, rubygem3.4-racc 1.8.1-31.hum1, +45 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
5 mo ago

Exploit prediction

0.43% chance of exploitation in the next 30 days, higher than 37% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 5.8 CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N
CNA 4.0 5.8 CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
rubygems net-imap
>=0.6.0, <0.6.4
>=0.5.0, <0.5.14
<0.4.24
0.6.4
0.5.14
0.4.24

Affected products

  • ruby net-imap

Classification

Weakness
  • CWE-93 Improper Neutralization of CRLF Sequences
  • CWE-77 Improper Neutralization of Special Elements used in a Command

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.