How severe is CVE-2026-42256?

No CVSS score has been assigned to CVE-2026-42256 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-42256?

CVE-2026-42256 affects the following packages: net-imap (RubyGems), net-imap (RubyGems), net-imap (RubyGems). Ecosystems affected: RubyGems.

How do I fix CVE-2026-42256?

Update net-imap to 0.6.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42256 is resolved across your whole dependency graph.

How do I detect CVE-2026-42256 in my RubyGems dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for net-imap, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-42256 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-42256?

O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-42256 can be triaged on real exposure rather than presence alone.

Is CVE-2026-42256 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-42256 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-42256?

CVE-2026-42256 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 23th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-42256?

CVE-2026-42256 is classified as CWE-770 (CWE-770), CWE-1322 (CWE-1322). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-42256 published, and has it been updated?

CVE-2026-42256 was published on May 9, 2026 and was last updated on September 14, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💎 RubyGems

Not in CISA KEV

CVE-2026-42256 — net-imap

Fix: ruby/net-imap@158d0b5

CVE-2026-42256 is a CWE-770 vulnerability in net-imap. A fix is available for net-imap — see the affected versions and patch details below.

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

Also known asGHSA-87pf-fpwv-p7m7

Published

May 9, 2026

Updated

Sep 14, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

Exploitation data as of Sep 19, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42256.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs23th percentile — riskier than 23% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Real-World Exposure

3 pkgs affected

💎net-imap💎net-imap💎net-imap

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.

Description

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.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
💎RubyGems	`net-imap`	≥ 0.6.0&&< 0.6.4	0.6.4`bundle update net-imap --conservative`
💎RubyGems	`net-imap`	≥ 0.5.0&&< 0.5.14	0.5.14`bundle update net-imap --conservative`
💎RubyGems	`net-imap`	≥ 0.4.0&&< 0.4.24	0.4.24`bundle update net-imap --conservative`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for net-imap, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update net-imap to 0.6.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42256 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-42256 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2026-42256. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Product	Fixed in	Advisory
Red Hat Enterprise Linux 10	`ruby4.0-0:4.0.6-36.el10_2`	RHSA-2026:50773
Red Hat Enterprise Linux 10	`ruby-0:3.3.12-14.el10_2`	RHSA-2026:50778
Red Hat Enterprise Linux 8	`ruby:3.3-8100020260727154509.489197e6`	RHSA-2026:50728
Red Hat Enterprise Linux 9	`ruby:4.0-9080020260727092509.9`	RHSA-2026:50827
Red Hat Enterprise Linux 9	`ruby:3.3-9080020260728061751.9`	RHSA-2026:50828
Red Hat Hardened Images	`ruby4-0-main-4.0.0-33.4.hum1`	RHSA-2026:33551
Red Hat Hardened Images	`ruby3-4-main-3.4.8-31.2.hum1`	RHSA-2026:33552
Red Hat Hardened Images	`ruby3-3-main-3.3.10-23.2.hum1`	RHSA-2026:33721

UbuntuMEDIUM

USN-8478-1Ubuntu

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2026-42256 in your dependencies?

O3 Security finds CVE-2026-42256 across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

Scan my dependencies How O3 SCA works