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UBUNTU-CVE-2026-4891
Vulnerability in dnsmasq (UBUNTU-CVE-2026-4891)
Summary
vulnerability in dnsmasq (UBUNTU-CVE-2026-4891). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to `2.90-0ubuntu0.16.04.1+esm3` or later.
AI summary snake-internal / snake-material-v2
A vulnerability tracked as **UBUNTU-CVE-2026-4891** has been found in dnsmasq.
Risk of unauthorized operations or information disclosure. CVSS score: ?/10.
What to do: upgrade dnsmasq to **2.90-0ubuntu0.16.04.1+esm3** or later.
If unsure, ask your IT team or search "dnsmasq UBUNTU-CVE-2026-4891" on the vendor's site.
UBUNTU-CVE-2026-4891 (dnsmasq) —
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: `2.90-0ubuntu0.16.04.1+esm3` — 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** (unclassified) exists in dnsmasq.
📍 Affected scope
dnsmasq — .
🔥 Severity
Severity: ?. Risk of unauthorized operations or information disclosure
🔧 How to fix
Update to **2.90-0ubuntu0.16.04.1+esm3**.
🛡️ 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 'dnsmasq' .` against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response Actions (7 steps)
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'dnsmasq' . | 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 `dnsmasq` を grep し、稼働しているサービス・バージョンを把握する。
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6Apply patch patch
Upgrade dnsmasq to 2.90-0ubuntu0.16.04.1+esm3ステージング環境で 2.90-0ubuntu0.16.04.1+esm3 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と、Step 3 で見つけた異常検知の続報チェックを含めること。
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7Post-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 Step 3 と同じログクエリでアラート再発が無いか継続監視。
Affected packages
Ubuntu:Pro:16.04:LTS
dnsmasq
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.90-0ubuntu0.16.04.1+esm3"}]}]
Ubuntu:Pro:18.04:LTS
dnsmasq
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.90-0ubuntu0.18.04.1+esm3"}]}]
Ubuntu:20.04:LTS
dnsmasq
[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}]
Ubuntu:22.04:LTS
dnsmasq
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.90-0ubuntu0.22.04.3"}]}]
Ubuntu:24.04:LTS
dnsmasq
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.90-2ubuntu0.3"}]}]
Ubuntu:25.10
dnsmasq
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.91-1ubuntu0.2"}]}]
Ubuntu:26.04
dnsmasq
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.92-1ubuntu0.2"}]}]
Ubuntu:Pro:20.04:LTS
dnsmasq
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.90-0ubuntu0.20.04.1+esm2"}]}]