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CVE-2026-42256 medium CVSS 6.5

Vulnerability in net-imap (CVE-2026-42256)

Summary

Vulnerability in net-imap (CVE-2026-42256). Risk of unauthorized operations or information disclosure. Exploitable via Timeout. Mitigation: upgrade to 0.4.24 or later.

Original description

The description as published by the source.

Summary

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.

Details

A hostile IMAP server can send an arbitrarily large PBKDF2 iteration count in the SCRAM server-first-message, causing the client to perform an expensive OpenSSL::KDF.pbkdf2_hmac call. Because the PBKDF2 function is a blocking C extension and holds onto Ruby’s Global VM Lock, it can freeze the entire Ruby VM for the duration of the computation.

OpenSSL enforces an effective maximum by using a 32-bit signed integer for the iteration count, Depending on hardware capabilities and OpenSSL version, this iteration count may be sufficient for to block all Ruby threads in the process for over seven minutes.

This is listed as one of the "Security Considerations", in RFC 7804:

A hostile server can perform a computational denial-of-service attack on clients by sending a big iteration count value. In order to defend against that, a client implementation can pick a maximum iteration count that it is willing to use and reject any values that exceed that threshold (in such cases, the client, of course, has to fail the authentication).

Impact

During SCRAM authentication to a hostile server, the entire Ruby VM will be locked for the duration of the computation. Depending on hardware capabilities…

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-2026-42256 has been found in net-imap.
Attackers can target a specific entry point like Timeout over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 6.5/10.
What to do: upgrade net-imap to 0.4.24 or later.
If unsure, ask your IT team or search "net-imap CVE-2026-42256" on the vendor's site.

CVE-2026-42256 (net-imap) — CWE-770 / CVSS v3 6.5
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: Timeout / max_iterations
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-770) exists in net-imap. Attackers reach the vulnerable code path via Timeout without authentication.

📍 Affected scope

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

🔥 Severity

Severity: Medium (CVSS 6.5/10). Risk of unauthorized operations or information disclosure.

🔧 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":"0.4.0"},{"fixed":"0.4.24"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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