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CVE-2026-42245 high CVSS 7.5

Vulnerability in net-imap (CVE-2026-42245)

Summary

Vulnerability in net-imap (CVE-2026-42245). Risk of unauthorized operations or information disclosure. Exploitable via ResponseReader. Mitigation: upgrade to 0.4.24 or later.

Original description

The description as published by the source.

Summary

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.

Details

For each literal in a response, ResponseReader rescans the entire growing response buffer. The regular expression that is used to scan the response buffer runs in linear time. With many literals, this becomes O(n²) total work. The regular expression should run in constant time: it is anchored to the end and only the last 23 bytes of the buffer are relevant.

Because the algorithmic complexity is super-linear, this bypasses protection from max_response_size: a response can stay well below the default size limit while still causing very large CPU cost.

Net::IMAP::ResponseReader runs continuously in the receiver thread until the connection closes.

Impact

This consumes disproportionate CPU time in the client's receiver thread. A hostile server could use this to exhaust the client's CPU for a denial of service attack.

For a response near the default max_response_size, each individual regexp scan could take between 100 to 200ms on common modern hardware, and this may be repeated 200k times per megabyte of response. While the regexp is scanning, it retains the Global VM lock, preventing other threads from running.

Although other threads should not be completely blocked, their run time will be significa…

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-2026-42245 has been found in net-imap.
Attackers can target a specific entry point like ResponseReader over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade net-imap to 0.4.24 or later.
If unsure, ask your IT team or search "net-imap CVE-2026-42245" on the vendor's site.

CVE-2026-42245 (net-imap) — CWE-407 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: ResponseReader / max_response_size
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-407) exists in net-imap. Attackers reach the vulnerable code path via ResponseReader without authentication.

📍 Affected scope

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

🔥 Severity

Severity: High (CVSS 7.5/10). 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"},{"fixed":"0.4.24"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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