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CVE-2026-42246 high CVSS 7.4

Vulnerability in net-imap (CVE-2026-42246)

Summary

Vulnerability in net-imap (CVE-2026-42246). Confidential information can be exposed externally. Exploitable via STARTTLS. Mitigation: upgrade to 0.3.10 or later.

Original description

The description as published by the source.

Summary

A man-in-the-middle attacker can cause Net::IMAP#starttls to return "successfully", without starting TLS.

Details

When using Net::IMAP#starttls to upgrade a plaintext connection to use TLS, a man-in-the-middle attacker can inject a tagged OK response with an easily predictable tag. By sending the response before the client finishes sending the command, the command completes "successfully" before the response handler is registered. This allows #starttls to return without error, but the response handler is never invoked, the TLS connection is never established, and the socket remains unencrypted.

This allows man-in-the-middle attackers to perform a STARTTLS stripping attack, unless the client code explicitly checks Net::IMAP#tls_verified?.

Impact

TLS bypass, leading to cleartext transmission of sensitive information.

Mitigation

  • Upgrade to a patched version of net-imap that raises an exception whenever #starttls does not establish TLS.
  • Connect to an implicit TLS port, rather than use STARTTLS with a cleartext port.
    This is strongly recommended anyway:
    • RFC 8314: Cleartext Considered Obsolete: Use of Transport Layer Security (TLS) for Email Submission and Access
    • NO STARTTLS: Why TLS is better without STARTTLS, A Security Analysis of STARTTLS in the Email Context
  • Explicitly verify Net::IMAP#tls_verified? is true, before using the connect…

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-42246 has been found in net-imap.
Attackers can target a specific entry point like STARTTLS over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 7.4/10.
What to do: upgrade net-imap to 0.3.10 or later.
If unsure, ask your IT team or search "net-imap CVE-2026-42246" on the vendor's site.

CVE-2026-42246 (net-imap) — CWE-392 / CVSS v3 7.4
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: STARTTLS / true
Patched: 0.3.10 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-392) exists in net-imap. Attackers reach the vulnerable code path via STARTTLS without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of net-imap. Attack surface: STARTTLS / true.

🔥 Severity

Severity: High (CVSS 7.4/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 0.3.10.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'net-imap' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'net-imap' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で net-imap を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade net-imap to 0.3.10

    ステージング環境で 0.3.10 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

rubygems net-imap
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.3.10"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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