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

CVE-2026-46348

HIGH · 8.7 CVSS v4.0 Published 2026-06-24
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
96/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click 8 weeks 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 4.5.10, 4.4.17, and 4.3.23, the list of disallowed IP address ranges was lacking an IP address range that can be used to reach local IP addresses. An attacker can use an IP address in the affected range to make Mastodon perform HTTP requests against loopback interfaces, potentially allowing access to otherwise private resources and services. This vulnerability is fixed in 4.5.10, 4.4.17, and 4.3.23.

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 · high confidence

This is a Server-Side Request Forgery (SSRF) vulnerability in Mastodon where the IP blocklist used to prevent internal network access was incomplete, missing a range that can be used to reach loopback interfaces (127.0.0.0/8). Attackers can abuse this to make Mastodon server perform HTTP requests to internal services bound to localhost, potentially exposing sensitive internal resources.

MitigationUpgrade Mastodon to version 4.5.10, 4.4.17, or 4.3.23 which contain the complete IP blocklist including the missing loopback range.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

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
Low
Privileges
None
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Determine installed Mastodon version
    Run 'git describe --tags' in the Mastodon directory, or check the VERSION file typically found at /home/mastodon/live/VERSION, or use the admin API endpoint /api/v1/instance if you have access
    Affected if The installed version is earlier than 4.5.10, 4.4.17, or 4.3.23 (e.g., 4.5.9, 4.4.16, etc.)
  2. Verify the instance accepts outgoing HTTP requests
    Check if the instance has features enabled that make outbound HTTP requests, such as OEmbed fetching, URL preview functionality, or any feature that fetches content from user-provided URLs
    Affected if The instance has any feature enabled that allows users to submit URLs for server-side fetching (URL preview, OEmbed, etc.)
  3. Inspect the IP blocklist configuration
    Locate the IP blocking or filtering configuration in the Mastodon codebase - typically in lib/mastodon/ip_blocklist.rb or similar, and verify whether 127.0.0.0/8 is included in the blocked ranges
    Affected if The IP blocklist does NOT include the 127.0.0.0/8 CIDR range, meaning loopback addresses are not blocked

Your instance is affected if it runs a Mastodon version prior to 4.5.10/4.4.17/4.3.23 AND has features enabled that allow user-supplied URLs to trigger server-side HTTP requests, AND the IP blocklist configuration is missing the 127.0.0.0/8 loopback range.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Mastodon to version 4.5.10, 4.4.17, or 4.3.23 which contain the complete IP blocklist including the missing loopback range.

Recommended fix High confidence

Upgrade to 4.5.10 (if on 4.5.x), 4.4.17 (if on 4.4.x), or 4.3.23 (if on 4.3.x or earlier)

  1. 1. Identify current Mastodon version by checking the /about page or running `git describe --tags` in the installation directory
  2. 2. Determine which upgrade path applies: if currently on 4.5.x, upgrade to 4.5.10; if on 4.4.x, upgrade to 4.4.17; if on 4.3.x or older, upgrade to 4.3.23 or later
  3. 3. Back up the Mastodon database and files before upgrading
  4. 4. For Docker installations: Update the image tag to the fixed version (e.g., `tootsuite/mastodon:v4.5.10`) and rebuild containers
  5. 5. For source installations: Run `git fetch --tags`, checkout the appropriate tag (e.g., `v4.5.10`), then run `bundle install` and `yarn install` followed by `RAILS_ENV=production bundle exec rails db:migrate`
  6. 6. Restart all Mastodon services (web, sidekiq, streaming)
  7. 7. Verify the upgrade by checking the version displayed on the /about page
Caveat Minor releases typically have no breaking changes; always review the release notes for the specific version before upgrading

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

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,560.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-46348 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2026-46348 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data