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CVE-2026-42258 medium CVSS 5.3

Command Injection in net-imap (CVE-2026-42258)

Summary

Command injection in net-imap (CVE-2026-42258). Data can be tampered with by attackers. Exploitable via flag. Mitigation: upgrade to 0.4.24 or later.

Original description

The description as published by the source.

Summary

Symbol arguments to commands are vulnerable to a CRLF Injection / IMAP Command injection via Symbol arguments passed to IMAP commands.

Details

Symbol arguments represent IMAP "system flags", which are formatted as "atoms" (with no quoting) with a "\" prefix. Vulnerable versions of Net::IMAP sends the symbol name directly to the socket, with no validation.

Because the Symbol input is unvalidated, it could contain invalid flag characters, including SP and CRLF, which could be used to finish the current command and inject new commands.

Although IMAP flag arguments are only valid input for a few IMAP commands, most Net::IMAP commands use generic argument handling, and will allow Symbol (flag) inputs.

Note also that the list of valid symbol inputs should be restricted to an enumerated set of standard RFC defined flag types, which have each been given specific defined semantics. Any user-provided values outside of that list of standard "system flags" needs to use the IMAP keyword syntax, which are sent as atoms, i.e: string inputs. Under no circumstances should #to_sym ever be called on unvetted user-provided input: that will always be a bug in the calling code for the simple reason that user_input_atom is as \user_input_atom.

For forward compatibility with future IMAP extentions, Net::IMAP, does not restrict flag inputs to an enumerated list. That is the responsibility of the calling application code, which knows which flag semantics…

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-2026-42258 has been found in net-imap.
Attackers can target a specific entry point like flag over the network to misuse the product.
Data can be tampered with by attackers. CVSS score: 5.3/10.
What to do: upgrade net-imap to 0.4.24 or later.
If unsure, ask your IT team or search "net-imap CVE-2026-42258" on the vendor's site.

CVE-2026-42258 (net-imap) — CWE-77 / CVSS v3 5.3
Attack vector: local / no user interaction
Attack surface: flag / CRLF / keyword / user_input_atom
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 flag.

📍 Affected scope

Check the vendor advisory for the affected versions of net-imap. Attack surface: flag / CRLF / keyword / user_input_atom.

🔥 Severity

Severity: Medium (CVSS 5.3/10). Data can be tampered with by attackers.

🔧 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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