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Fencer Vulns
medium 6.5

CVE-2026-42256 json

net-imap: Denial of service via high iteration count for `SCRAM-*` authentication

published 2026-05-04 6 mo ago modified 2026-09-10 1 mo ago also EUVD-2026-28925 , GHSA-87pf-fpwv-p7m7

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 22%
public exploits
0
none known

Summary

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. From versions 0.4.0 to before 0.4.24, 0.5.0 to before 0.5.14, and 0.6.0 to before 0.6.4, when authenticating a connection with SCRAM-SHA1 or SCRAM-SHA256, a hostile server can perform a computational denial-of-service attack on the client process by sending a big iteration count value. 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-2026-42256

  • ruby3.3 Ubuntu 26.04 LTS 3.3.8-2ubuntu3.1

ubuntu advisories UBUNTU-CVE-2026-42256

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-2026:38694

  • rmt-server SLE Module for Server Applications 15 SP7, SLE Module for Public Cloud 15 SP7 3.1.0-150700.3.28.1

suse advisories SUSE-SU-2026:3792-1

  • rmt-server openSUSE Leap 16.0 3.0.0-160000.1.1

opensuse advisories openSUSE-SU-2026:21225-1

  • 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-2026-42256

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-2026-42256 updated cvss 6.5

ruby/net-imap: ruby: Net::IMAP: Denial of Service via large iteration count in SCRAM authentication

  • 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: workaround, no fix available “Fix deferred”
  • 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 ruby3.4 3.4.10-31.hum1, ruby3.4 3.4.8-31.2.hum1, ruby4.0 4.0.0-33.4.hum1, ruby3.3 3.3.10-23.2.hum1, ruby3.4-libs 3.4.10-31.hum1, ruby3.4-libs 3.4.8-31.2.hum1, +78 more
    fixed: vendor fix RHSA-2026:33721

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

0.30% chance of exploitation in the next 30 days, higher than 22% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 6.0 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CNA 4.0 6.0 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:H/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 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
rubygems net-imap
>=0.6.0, <0.6.4
>=0.5.0, <0.5.14
>=0.4.0, <0.4.24
0.6.4
0.5.14
0.4.24

Affected products

  • ruby net-imap

Classification

Weakness
  • CWE-1322 Use of Blocking Code in Single-threaded, Non-blocking Context
  • CWE-770 Allocation of Resources Without Limits or Throttling

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.