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Improper Input ValidationWeakness · CWE-20

CVE-2026-33250

HIGH · 7.5 CVSS v3.1 Published 2026-03-24
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click Patch available

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
Freeciv21 is a free open source, turn-based, empire-building strategy game. Versions prior to 3.1.1 crash with a stack overflow when receiving specially-crafted packets. A remote attacker can use this to take down any public server. A malicious server can use this to crash the game on the player's machine. Authentication is not needed and, by default, logs do not contain any useful information. All users should upgrade to Freeciv21 version 3.1.1. Running the server behind a firewall can help mitigate the issue for non-public servers. For local games, Freeciv21 restricts connections to the current user and is therefore not affected.

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-20

The application accepts input without confirming it is well-formed or within expected bounds, so malformed data can push the program into states its author never anticipated. Attackers probe these gaps to trigger crashes, bypass logic, or feed tainted values into more dangerous operations downstream. Remediating it well means validating and normalising every input at the boundary against a strict allow-list — not merely filtering known-bad values.

General guidance for the improper input validation 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
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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
Patch available Apply the vendor patch
Vendor patch github.com →
Recommended fix High confidence

Freeciv21 3.1.1

  1. Check the currently installed Freeciv21 version (client and server)
  2. If the version is prior to 3.1.1, download Freeciv21 version 3.1.1 from the official source at https://github.com/longturn/freeciv21/releases
  3. Upgrade both the Freeciv21 client and server installations to version 3.1.1
  4. Restart the server if running a server instance
  5. Verify the upgrade was successful by checking the version number

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

We can apply and verify the patch for your build — typical engagement from $1,950. Get the patch applied

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Free · runs locally
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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-2026-33250 in production — separate from our analysis above.

No notes yet

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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
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