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CVE Record

CVE-2026-42246: net-imap vulnerable to STARTTLS stripping via invalid response timing

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to versions 0.3.10, 0.4.24, 0.5.14, and 0.6.4, a man-in-the-middle attacker can cause Net::IMAP#starttls to return "successfully", without starting TLS. This issue has been patched in versions 0.3.10, 0.4.24, 0.5.14, and 0.6.4.

HighCVSS 7.6Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

Ruby applications using vulnerable net-imap versions can be fooled into thinking STARTTLS succeeded when it did not. A network-positioned attacker could then observe or alter IMAP traffic that operators expected to be encrypted. This matters most for systems handling mailbox credentials or sensitive email over untrusted networks.

Executive priority

Treat this as a high-priority dependency update for Ruby services that access email. The main business risk is silent loss of expected mail-channel encryption, exposing credentials or sensitive email contents to network attackers.

Technical view

CVE-2026-42246 affects Ruby net-imap before 0.3.10, 0.4.24, 0.5.14, and 0.6.4. A man-in-the-middle can abuse invalid response timing so Net::IMAP#starttls returns successfully without establishing TLS. The CVSS v4.0 score is 7.6, with high confidentiality and integrity impact.

Likely exposure

Exposure is limited to Ruby applications or packaged platforms using affected net-imap versions and STARTTLS for IMAP connections. Systems using patched gem versions or unaffected downstream packages are not indicated as exposed by the provided sources.

Exploitation context

The bundle does not indicate KEV listing or confirmed active exploitation. Exploitation requires a man-in-the-middle position and a victim application path that initiates STARTTLS using vulnerable Net::IMAP behavior.

Researcher notes

The key behavior is a false-success STARTTLS state in Net::IMAP#starttls. The sources provide affected version ranges, patched releases, commits, and Red Hat downstream advisories, but no proof-of-concept, active exploitation claim, or broader affected product list.

Mitigation direction

  • Upgrade net-imap to 0.3.10, 0.4.24, 0.5.14, 0.6.4, or later matching your branch.
  • Apply relevant Red Hat security advisories for packaged Ruby or net-imap components.
  • Inventory applications and images that include Ruby net-imap dependencies.
  • Check vendor guidance where net-imap is bundled by a distribution or product.

Validation and detection

  • Review Gemfile.lock, gemspecs, SBOMs, and container images for affected net-imap versions.
  • Identify code paths that call Net::IMAP#starttls for mailbox connections.
  • Confirm production and staging dependency resolution now selects a patched net-imap release.
  • For Red Hat systems, compare installed packages against the listed RHSA advisories.
Prepared
Confidence
high
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-325: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cwe · low confidence lookup

CWE-392: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cwe · low confidence lookup

CWE-393: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cwe · low confidence lookup

CWE-636: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cwe · low confidence lookup

CWE-754: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cwe · low confidence lookup

CWE-841: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.6 (4.0)
Known Exploited
No
Published

Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
32Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: total

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.6CVSS 4.0HighCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N——GitHub_M
7.4CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N2.25.2redhat-SADP

Vulnerability scoring details

Base CVSS 4.0 score

7.6High
CVSS 4.0 vector shape for CVE-2026-42246Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPnet-imap: ruby: Net::IMAP: Information disclosure via man-in-the-middle attack bypassing TLS
other:Red Hat severity ratingcvssV3_1
  • 2026-05-09T20:01:04.782Z: Reported to Red Hat.
  • 2026-05-09T19:33:17.880Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
rubynet-imap< 0.3.10, >= 0.4.0, < 0.4.24, >= 0.5.0, < 0.5.14, >= 0.6.0, < 0.6.4Listed
Weakness

CWE details

CWE-325CWE-392CWE-393CWE-636CWE-754CWE-841

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.