Vulnerability in Mastodon (CVE-2026-47389)
Summary
Vulnerability in Mastodon (CVE-2026-47389). Confidential information can be exposed externally. Mitigation: upgrade to 4.5.10 or later.
Original description
The description as published by the source.
Mastodon is a free, open-source social network server based on ActivityPub. Prior to 4.5.10, 4.4.17, and 4.3.23, when using Ruby versions older than 3.4, PrivateAddressCheck.private_address? returns false for IPv4-mapped IPv6 addresses (::ffff:a.b.c.d) corresponding to some private IPv4 addresses, depending on Ruby version, this can include loopback, RFC1918 private networks, and link-local space. An attacker who controls DNS for any domain can publish an AAAA record with such a mapped address; any outbound HTTP fetch Mastodon performs against that hostname then opens a real TCP connection to the underlying IPv4 address, including 127.0.0.1 and cloud-metadata endpoints such as 169.254.169.254. This vulnerability is fixed in 4.5.10, 4.4.17, and 4.3.23.
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-2026-47389 has been found in Mastodon.
Confidential information can be exposed externally. CVSS score: 8.6/10.
What to do: upgrade Mastodon to 4.5.10 or later.
If unsure, ask your IT team or search "Mastodon CVE-2026-47389" on the vendor's site.
CVE-2026-47389 (Mastodon) — CWE-184 / CVSS v3 8.6
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 4.5.10 — 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.
A vulnerability (CWE-184) exists in Mastodon.
Check the vendor advisory for the affected versions of Mastodon.
Severity: High (CVSS 8.6/10). Confidential information can be exposed externally.
Update to 4.5.10.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'Mastodon' . 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
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1Identify exposure identify
grep -r 'Mastodon' . | 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
Mastodonを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade Mastodon to 4.5.10ステージング環境で 4.5.10 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。
-
3Post-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。
References
- advisory github.com
- advisory github.com
- advisory nvd.nist.gov