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CVE-2026-42257 critical CVSS 9.8

Command Injection in net-imap (CVE-2026-42257)

Summary

Command injection in net-imap (CVE-2026-42257). Successful exploitation can lead to full system takeover. Exploitable via CRLF. Mitigation: upgrade to 0.4.24 or later.

Original description

The description as published by the source.

Summary

Several Net::IMAP commands accept a raw string argument that is sent to the server without validation or escaping. If this string is derived from user-controlled input, it may contain contain CRLF sequences, which an attacker can use to inject arbitrary IMAP commands.

Details

Net::IMAP's generic argument handling, used by most command arguments, interprets string arguments as an IMAP astring. Depending on the string contents and the connection's UTF-8 support, this encodes strings as either a atom, quoted, or literal. These are safe from command or argument injection.

But the following commands transform specific String arguments to Net::IMAP::RawData, which bypasses normal argument validation and encoding and prints the string directly to the socket:

  • #uid_search, #search, #uid_sort, #sort, #uid_thread, #thread
    • when criteria is a String, it is sent raw
  • #uid_fetch, `#fetch
    • when attr is a String, it is sent raw
    • when attr is an Array, each String in attr is sent raw
  • #uid_store, #store
    • when attr is a String, it is sent raw
  • #setquota:
    • limit is interpolated with #to_s and that string is sent raw

Because these string arguments are sent without any neutralization, they serve as a direct vector for command splitting. Any user controlled data interpolated into these strings can be used to break out of the intended command context.

Using "raw data" arguments for #uid_store, `#stor…

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-2026-42257 has been found in net-imap.
Attackers can target a specific entry point like CRLF over the network to misuse the product.
Successful exploitation can lead to full system takeover. CVSS score: 9.8/10.
What to do: upgrade net-imap to 0.4.24 or later.
If unsure, ask your IT team or search "net-imap CVE-2026-42257" on the vendor's site.

CVE-2026-42257 (net-imap) — CWE-77 / CVSS v3 9.8
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: CRLF / astring / atom / quoted
Patched: 0.4.24 — 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-77) exists in net-imap. Attackers reach the vulnerable code path via CRLF without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of net-imap. Attack surface: CRLF / astring / atom / quoted.

🔥 Severity

Severity: Critical (CVSS 9.8/10). Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to 0.4.24.

🛡️ 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 0.4.24

    ステージング環境で 0.4.24 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":"0.4.24"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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