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Config LibApplication · Config Lib Project

CVE-2021-37632

HIGH · 8.1 CVSS v3.1 Published 2021-08-05
Fix available
A fix is available. Upgrade to 1.0.9 or later.
See remediation →
90/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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
SuperMartijn642's Config Lib is a library used by a number of mods for the game Minecraft. The versions of SuperMartijn642's Config Lib between 1.0.4 and 1.0.8 are affected by a vulnerability and can be exploited on both servers and clients. Using SuperMartijn642's Config Lib, servers will send a packet to clients with the server's config values. In order to read `enum` values from the packet data, `ObjectInputStream#readObject` is used. `ObjectInputStream#readObject` will instantiate a class based on the input data. Since, the packet data is not validated before `ObjectInputStream#readObject` is called, an attacker can instantiate any class by sending a malicious packet. If a suitable class is found, the vulnerability can lead to a number of exploits, including remote code execution. Although the vulnerable packet is typically only send from server to client, it can theoretically also be send from client to server. This means both clients and servers running SuperMartijn642's Config Lib between 1.0.4 and 1.0.8 are vulnerable. The vulnerability has been patched in SuperMartijn642's Config lib 1.0.9. Both, players and server owners, should update to 1.0.9 or higher.

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

SuperMartijn642's Config Lib uses ObjectInputStream#readObject to deserialize enum values from network packets without validating the input data. This allows an attacker to send malicious serialized objects that instantiate arbitrary Java classes, potentially leading to remote code execution via deserialization gadget chains.

MitigationUpdate SuperMartijn642's Config Lib to version 1.0.9 or higher in all affected Minecraft mods on both servers and clients.

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

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Config LibApplication
Affected:>= 1.0.4, < 1.0.9

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
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

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. Locate the Config Lib library in your Minecraft mod environment
    Search for files named 'ConfigLib-*.jar' or classes containing 'supermartijn642/configlib' in your mods folder or classpath. Check both server and client mod directories.
    Affected if The library file or class is found and its version is >= 1.0.4 and < 1.0.9.
  2. Identify the exact version of SuperMartijn642's Config Lib
    Open the JAR file's manifest (META-INF/MANIFEST.MF) or the mod's metadata to read the 'Implementation-Version' or 'Version' attribute. Alternatively, check the JAR filename if it includes the version number.
    Affected if The version string starts with 1.0.4, 1.0.5, 1.0.6, 1.0.7, or 1.0.8.
  3. Determine if your mods depend on Config Lib for network config synchronization
    Inspect your installed mods' mod.toml or mods.toml files for 'supermartijn642:configlib' in the dependencies section. Check mod source code for calls to ConfigLib's configuration reading methods that accept network input.
    Affected if Any installed mod lists Config Lib as a dependency and uses network-based config sync features.
  4. Verify if the server or client accepts config data from network sources
    Review server logs for incoming packet data handled by Config Lib during mod initialization. On the client, check if the server pushes configuration updates. Look for log messages containing 'config' and 'sync' from the configlib package.
    Affected if Network config synchronization is enabled and the vulnerable code path is actively deserializing data.

You are affected if SuperMartijn642's Config Lib version 1.0.4 through 1.0.8 is present AND any mod uses it to deserialize config data from network packets.

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.

From vendor data
Upgrade available Upgrade to 1.0.9 or later
Fixed in 1.0.9
Interim mitigation

Update SuperMartijn642's Config Lib to version 1.0.9 or higher in all affected Minecraft mods on both servers and clients.

Fix this in Config Lib Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.

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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-2021-37632 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
  • No spam, self-promotion, credentials, or personal data