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Full vulnerability report · 2026
CVE-2026-42245High confidence

net-imap: Quadratic complexity when reading response literals

ruby · net-imap

Official source article: GitHub GHSA-Q2MW-FVJ9-VVCW ↗. Check the applicable product and release in the original source.

2.3LowCVSS 4.0
Recommended action
Patch only the product branches with a verified fix

Low technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 4 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityLowOperational priority:Low, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • EPSS is 0.70% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs ruby net-imap and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: No default targetRemediation target: Normal maintenance

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Cross-source reconciliation

Remediation availability differs by product scope

Verified remediation exists for at least one product or source, but 4 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Distribution package intelligence

Release-specific package status

Debian findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

4 package states
Package result overrides the generic status

BlackTree has verified remediation for at least one product or source, but the relevant distribution still reports no fixed package for 4 affected package states shown here. Treat those rows as affected with no fix until that distribution publishes a fixed version.

Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Debian trixietrixie · sourceruby3.3Affected, no fix publishedDebian currently tracks this release as open.Not published in this feedDebian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourceruby3.1Affected, no fix publishedDebian currently tracks this release as open.Not published in this feedDebian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourceruby3.3Affected, no fix publishedDebian currently tracks this release as open.Not published in this feedDebian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourceruby3.3Affected, no fix publishedDebian currently tracks this release as open.Not published in this feedDebian Security Tracker ↗Source updated 5 Oct 2026
Open-source package ranges6 source-attributed ranges

These OSV and GitHub advisory ranges apply only to the named package and ecosystem. A listed fixed version is not a universal product patch or proof that an update is installed.

Ecosystem and packageAffected rangeFirst fixed versionEvidence
RubyGemsnet-imapECOSYSTEM: introduced 0.6.0; fixed 0.6.40.6.4OSV record ↗aggregator derived · 10 Sep 2026
RubyGemsnet-imapECOSYSTEM: introduced 0.5.0; fixed 0.5.140.5.14OSV record ↗aggregator derived · 10 Sep 2026
RubyGemsnet-imapECOSYSTEM: introduced 0; fixed 0.4.240.4.24OSV record ↗aggregator derived · 10 Sep 2026
rubygemsnet-imap>= 0.6.0, <= 0.6.30.6.4GitHub advisory ↗upstream repository advisory · 14 May 2026
rubygemsnet-imap>= 0.5.0, <= 0.5.130.5.14GitHub advisory ↗upstream repository advisory · 14 May 2026
rubygemsnet-imap>= 0, <= 0.4.230.4.24GitHub advisory ↗upstream repository advisory · 14 May 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-42245 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityruby: net-imap: Net::IMAP: Denial of Service via crafted IMAP responses
954 fixed

The vendor explicitly identifies these products or versions as containing the fix.

  • ruby-0:3.3.10-11.el10_0.2.aarch64 as a component of Red Hat Enterprise Linux AppStream EUS (v. 10.0)
  • ruby-0:3.3.10-11.el10_0.2.ppc64le as a component of Red Hat Enterprise Linux AppStream EUS (v. 10.0)
  • ruby-0:3.3.10-11.el10_0.2.s390x as a component of Red Hat Enterprise Linux AppStream EUS (v. 10.0)
  • ruby-0:3.3.10-11.el10_0.2.src as a component of Red Hat Enterprise Linux AppStream EUS (v. 10.0)
  • ruby-0:3.3.10-11.el10_0.2.x86_64 as a component of Red Hat Enterprise Linux AppStream EUS (v. 10.0)
  • ruby-bundled-gems-0:3.3.10-11.el10_0.2.aarch64 as a component of Red Hat Enterprise Linux AppStream EUS (v. 10.0)
  • ruby-bundled-gems-0:3.3.10-11.el10_0.2.ppc64le as a component of Red Hat Enterprise Linux AppStream EUS (v. 10.0)
  • ruby-bundled-gems-0:3.3.10-11.el10_0.2.s390x as a component of Red Hat Enterprise Linux AppStream EUS (v. 10.0)
  • ruby-bundled-gems-0:3.3.10-11.el10_0.2.x86_64 as a component of Red Hat Enterprise Linux AppStream EUS (v. 10.0)
  • ruby-bundled-gems-debuginfo-0:3.3.10-11.el10_0.2.aarch64 as a component of Red Hat Enterprise Linux AppStream EUS (v. 10.0)
  • ruby-bundled-gems-debuginfo-0:3.3.10-11.el10_0.2.ppc64le as a component of Red Hat Enterprise Linux AppStream EUS (v. 10.0)
  • ruby-bundled-gems-debuginfo-0:3.3.10-11.el10_0.2.s390x as a component of Red Hat Enterprise Linux AppStream EUS (v. 10.0)
Summary
A flaw was found in Net::IMAP, a Ruby library implementing the Internet Message Access Protocol (IMAP) client functionality. A hostile server can exploit a quadratic time complexity issue in the `Net::IMAP::ResponseReader` when processing large responses containing numerous string literals. This can lead to the client's CPU being exhausted, resulting in a denial of service (DoS) attack.
Remediation
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-28923

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch only the product branches with a verified fix

Low technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 4 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
01

What, why and how

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.

What

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

An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.

How

An attacker operating through a network path may attempt exploitation when the stated preconditions are met. If successful, the issue may disrupt the affected service.

What

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

An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.

How

An attacker operating through a network path may attempt exploitation when the stated preconditions are met. If successful, the issue may disrupt the affected service.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Inefficient Algorithmic Complexity → disrupt the affected service
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
Passive interaction required
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Not a CVSS 4.0 base metric
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-407 ↗

CWE-407: Inefficient Algorithmic Complexity. An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Common Vulnerability Scoring System 4.0: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.ATPresentAttack requirements: A particular deployment or execution condition must be present.PRNonePrivileges required: The attacker does not need an account or existing privileges.UIPassiveUser interaction: A user must unknowingly interact with the vulnerable system.VCNoneVulnerable-system confidentiality: No direct loss is represented by this metric.VINoneVulnerable-system integrity: No direct loss is represented by this metric.VALowVulnerable-system availability: A successful attack can cause a limited loss.SCNoneSubsequent-system confidentiality: No direct loss is represented by this metric.SINoneSubsequent-system integrity: No direct loss is represented by this metric.SANoneSubsequent-system availability: No direct loss is represented by this metric.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedDenial of serviceCWE-407
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

BSI · German · WID-SEC-2026-2379Ruby: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Ruby ausnutzen, um Informationen offenzulegen, um einen Denial of Service Angriff durchzuführen, und um beliebigen Programmcode auszuführen.

Official advisory ↗
BSI · German · WID-SEC-2026-2117HCL BigFix Compliance (Ruby): Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in HCL BigFix Compliance ausnutzen, um beliebigen Code auszuführen, Sicherheitsmaßnahmen zu umgehen, Daten zu manipulieren, vertrauliche Informationen offenzulegen oder einen Denial-of-Service-Zustand herbeizuführen.

Official advisory ↗
BSI · German · WID-SEC-2026-2163Red Hat Enterprise Linux (ruby: net-imap): Mehrere Schwachstellen

Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Red Hat Enterprise Linux ausnutzen, um einen Denial of Service Angriff durchzuführen, Sicherheitsmaßnahmen zu umgehen, Daten zu manipulieren oder vertrauliche Informationen offenzulegen.

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-0958Multiples vulnérabilités dans les produits IBM

d?id=CVE-2026-42036 Référence CVE CVE-2026-42037 https://www.cve.org/CVERecord?id=CVE-2026-42037 Référence CVE CVE-2026-42038 https://www.cve.org/CVERecord?id=CVE-2026-42038 Référence CVE CVE-2026-42039 https://www.cve.org/CVERecord?id=CVE-2026-42039 Référence CVE CVE-2026-42040 https://www.cve.org/CVERecord?id=CVE-2026-42040 Référence CVE CVE-2026-42041 https://www.cve.org/CVERecord?id=CVE-2026-42041 Référence CVE CVE-2026-42042 https://www.cve.org/CVERecord?id=CVE-2026-42042 Référence CVE CVE-2026-42043 https://www.cve.org/CVERecord?id=CVE-2026-42043 Référence CVE CVE-2026-42044 https://www.cve.org/CVERecord?id=CVE-2026-42044 Référence CVE CVE-2026-42245 https://www.cve.org/CVERecord?id=CVE-2026-42245 Référence CVE CVE-2026-42246 https://www.cve.org/CVERecord?id=CVE-2026-42246 Référence CVE CVE-2026-42253 https://www.cve.org/CVERecord?id=CVE-2026-42253 Référence CVE CVE-2026-42256 https://www.cve.org/CVERecord?id=CVE-2026-42256 Référence CVE CVE-2026-42257 https://www.cve.org/CVERecord?id=CVE-2026-42257 Référence CVE CVE-2026-42258 https://www.cve.org/CVERecord?id=CVE-2026-42258 Référence CVE CVE-2026-42264 https://www.cve.org/CVERecord?id=CVE-2026-42264 Référence CVE CVE-2026-42338 https://www.cve.org/CVERecord?id=CVE-2026-42338 Référence CVE CVE-2026-42502 https://www.cve.org/CVERecord?id=

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-016430Ruby-lang.orgのNet::IMAPにおけるアルゴリズムの複雑さに関する脆弱性

Net::IMAPはRubyでインターネットメッセージアクセスプロトコル（IMAP）クライアント機能を実装しています。バージョン0.4.24、0.5.14、0.6.4より前のバージョンでは、多数の文字列リテラルを含む大きな応答を読み取る際にNet::IMAP::ResponseReaderが二次時間計算量を有していました。悪意のあるサーバーは、クライアントのCPUを消耗させるように細工された応答を送信し、サービス拒否攻撃を実行することができます。この問題はバージョン0.4.24、0.5.14、0.6.4で修正されています。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Fix availability varies by product
Affected
net-imap: < 0.4.24, >= 0.5.0, < 0.5.14, >= 0.6.0, < 0.6.4
Fixed
Action
Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
Workaround
A mitigation or workaround reference is available from the source linked below; validate it against the affected product and version.
04

Evidence and provenance

Published 9 May 2026 · Last source change 12 May 2026, 18:30 UTC · CWE-407 · Inefficient Algorithmic Complexity

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-28923
Product sourceCNA
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    < 0.4.24; >= 0.5.0, < 0.5.14; >= 0.6.0, < 0.6.4 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
    After
    < 0.4.24; >= 0.5.0, < 0.5.14; >= 0.6.0, < 0.6.4 · Fixed: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
    Red Hat Product Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
Fixed release recorded from official guidance
ENISA EUVD · EUVD-2026-28923↗Red Hat Product Security security advisory↗CVE authority or vendor reference · GitHub GHSA-Q2MW-FVJ9-VVCW↗Patch or update reference↗Patch or update reference↗Patch or update reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-42245 · cve.blacktree.nl