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Server-Side Request Forgery (SSRF)Weakness · CWE-918

CVE-2026-72916

MEDIUM · 6.3 CVSS v4.0 Published 2026-08-10
No fix yet
No fix has been published. The vendor has not shipped a fixed release or patch. You remain exposed.
See remediation →
72/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click 8 days old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Mastodon is a free, open-source social network server based on ActivityPub. Prior to 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1, PrivateAddressCheck.private_address? in app/lib/private_address_check.rb normalized IPv4-mapped IPv6 addresses but did not recognize IPv4-compatible IPv6 addresses with IPAddr#ipv4_compat?. An attacker could supply an address in the omitted range to bypass the ALLOWED_PRIVATE_ADDRESSES protection and make Mastodon send HTTP requests to loopback interfaces, potentially accessing private resources and services. Exploitation requires a system that supports the obsolete IPv4-compatible IPv6 mechanism. This issue is fixed in versions 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-918

The server can be induced to make requests to a URL an attacker controls, turning it into a proxy into internal networks and cloud metadata services. It's especially dangerous behind a trusted network boundary. The fix is strict allow-listing of destinations and blocking access to internal address ranges.

General guidance for the server-side request forgery (ssrf) class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
High
Privileges
None
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Recommended fix High confidence

Upgrade to 4.6.4 (latest stable) or the appropriate version in your current release branch (4.4.21 for 4.4.x, 4.5.14 for 4.5.x, 4.6.4 for 4.6.x, 4.7.0-beta.1 for beta)

  1. Backup your Mastodon database and uploaded files before upgrading
  2. Identify your current Mastodon version (check version file or admin interface)
  3. Review the official Mastodon upgrade guide at https://docs.joinmastodon.org/admin/upgrading/
  4. Stop the Mastodon services (web, sidekiq, streaming)
  5. Update your Mastodon installation to version 4.4.21, 4.5.14, 4.6.4, or 4.7.0-beta.1 depending on your current version branch
  6. Run database migrations with RAILS_ENV=production bundle exec rails db:migrate
  7. Precompile assets with RAILS_ENV=production bundle exec rails assets:precompile
  8. Restart Mastodon services
Caveat Check release notes for your target version for any breaking changes; major version jumps may require additional migration steps

Generated from the published advisory — verify against the referenced sources before acting.

No vendor fix exists The vendor has not published a patch for this.

There is no version to upgrade to and no patch to apply. Every affected install stays exposed until the vendor ships a fix — or somebody else builds one.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-72916 in production — separate from our analysis above.

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What this is

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What belongs here
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