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NethackApplication

CVE-2020-5211

CRITICAL · 9.8 CVSS v3.1 Published 2020-01-28
Fix available
A fix is available. Upgrade to 3.6.5 or later.
See remediation →
100/100
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
In NetHack before 3.6.5, an invalid extended command in value for the AUTOCOMPLETE configuration file option can cause a buffer overflow resulting in a crash or remote code execution/privilege escalation. This vulnerability affects systems that have NetHack installed suid/sgid and shared systems that allow users to upload their own configuration files. Users should upgrade to NetHack 3.6.5.

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

In NetHack before 3.6.5, the AUTOCOMPLETE configuration file option does not properly validate extended command values, allowing an invalid input to trigger a buffer overflow. On systems where NetHack is installed with suid/sgid permissions, this can lead to privilege escalation, and on shared systems where users can upload custom config files, it enables remote code execution.

MitigationUpgrade to NetHack 3.6.5 immediately. On shared systems, restrict or audit user-provided configuration files. Consider removing suid/sgid bits from NetHack installations if not strictly required.

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
NethackApplication
Affected:< 3.6.5

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
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/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 NetHack installation
    Run 'which nethack' or 'which NetHack' to find the executable path, or check common locations like /usr/games/nethack, /usr/bin/nethack
    Affected if NetHack is not found on the system - not applicable
  2. Determine installed NetHack version
    Run 'nethack --version' or check the binary with 'nethack -version'. Also check package manager: 'dpkg -l | grep nethack' (Debian) or 'rpm -qa | grep nethack' (RHEL)
    Affected if Version is lower than 3.6.5 (e.g., 3.6.4, 3.6.3, etc.)
  3. Check for user-writable configuration files
    Inspect NetHack config files: look for ~/.nethackrc, ~/.config/nethack, or /etc/nethackrc. Check file permissions with 'ls -la' to see if other users can modify these files
    Affected if Users other than the owner can write to NetHack configuration files, enabling malicious config injection
  4. Verify binary permissions (suid/sgid)
    Run 'ls -l $(which nethack)' to check if the NetHack binary has setuid or setgid bits set
    Affected if The nethack binary has suid (setuid) or sgid (setgid) permissions, which could allow privilege escalation
  5. Check for AUTOCOMPLETE directive in config
    Search config files for the string 'AUTOCOMPLETE' using 'grep -r AUTOCOMPLETE ~/.nethackrc ~/.config/nethack/ /etc/nethackrc 2>/dev/null'
    Affected if An AUTOCOMPLETE directive exists with potentially malformed extended command values

You are affected if NetHack version is below 3.6.5 AND you use custom configuration files with the AUTOCOMPLETE option, especially on systems where the binary has suid/sgid permissions.

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
Upgrade available Upgrade to 3.6.5 or later
Fixed in 3.6.5
Interim mitigation

Upgrade to NetHack 3.6.5 immediately. On shared systems, restrict or audit user-provided configuration files. Consider removing suid/sgid bits from NetHack installations if not strictly required.

Recommended fix High confidence

NetHack 3.6.5

  1. Check the current installed NetHack version using 'nethack --version' or similar command
  2. Obtain NetHack version 3.6.5 from the official NetHack distribution channels (such as GitHub or official NetHack websites)
  3. Backup any existing NetHack configuration files if desired
  4. Install NetHack 3.6.5 using the appropriate package manager or compilation process for your system
  5. If NetHack was previously installed with suid/sgid permissions, verify and restore the correct permissions after upgrading (e.g., chmod u+s and chmod g+s on the NetHack binary)
  6. Verify the new version is installed correctly by running 'nethack --version'

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

Fix this in Nethack Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
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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-2020-5211 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