CVE-2026-42245: Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby

This month

HIGH 7.5REMOTEUPGRADE

CVE-2026-42245 is a high-severity flaw (CVSS 7.5) affecting net\. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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, Net::IMAP::ResponseReader has quadratic time complexity when reading large responses containing many string literals. A hostile server can send responses which are crafted to exhaust the client's CPU for a denial of service attack. This issue has been patched in versions 0.4.24, 0.5.14, and 0.6.4.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 65%)
CISA exploited list	No
Weakness	CWE-407
Published	2026-05-09
Last modified	2026-07-24

Publisher (CNA): GitHub, Inc. · Vendor: ruby-lang

Last updated 2026-07-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-09 20:16 UTCPublished CVE record published
2026-07-24 19:10 UTCUpdated Record last modified

ruby-lang net\ UPGRADE

Affected: < 0.4.24 · >= 0.5.0 and < 0.5.14 · >= 0.6.0 and < 0.6.4

Fixed in: 0.4.24, 0.5.14, 0.6.4

Safe to downgrade to: a release before 0.5.0

1. Check installed version

apt-cache policy net || rpm -q net || net --version

2. UPGRADE to 0.4.24 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade net

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade net

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 0.5.0 (Debian / Ubuntu)

apt-cache madison net sudo apt install net=<VERSION_BEFORE_0.5.0> sudo apt-mark hold net

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list net sudo dnf downgrade net-<VERSION_BEFORE_0.5.0> sudo dnf versionlock add net

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Advisories and coverage

Official advisories

Ruby News: Ruby 3.3.12 Released 2026-07-16
AlmaLinux Errata: [ALSA-2026:33576] Important: ruby:3.3 security update 2026-07-01
AlmaLinux Errata: [ALSA-2026:33577] Important: ruby:4.0 security update 2026-07-01

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-42245?

net\: upgrade to 0.4.24, 0.5.14, 0.6.4. Exact commands for each OS are on this page.

Is CVE-2026-42245 being exploited?

CVE-2026-42245 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-42245 affect?

CVE-2026-42245 affects net\. Severity is high (CVSS 7.5). 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, Net::IMAP::ResponseReader has quadratic time complexity when reading large responses containing many str

How urgent is CVE-2026-42245?

Priority 40/100. High severity; Remotely exploitable, no login, no user action

Software pages

Ruby vulnerabilities

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References

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