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X11r6Application · Xfree86 Project

CVE-1999-0241

HIGH · 10.0 CVSS v2.0 Published 1995-11-01
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
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
Guessable magic cookies in X Windows allows remote attackers to execute commands, e.g. through xterm.

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 · moderate confidence

X Windows (X11) uses MIT-MAGIC-COOKIE-1 authentication tokens to authorize client connections to the X server. This vulnerability exists when these magic cookies are guessable or can be derived, allowing remote attackers to connect to the X server and execute commands (e.g., through xterm) without proper authorization.

MitigationRestrict X server access using xhost/xauth controls, firewall rules, or SSH X11 forwarding; disable direct X access over network or upgrade to more secure authentication mechanisms like SUN-DES-1 or Kerberos.

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
X11r6Application
Affected:all versions
IrixOperating system
Affected:all versions
SolarisOperating system
Affected:= 2.5= 2.5.1= 7.0
SunosOperating system
Affected:all versions

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
Authentication
None
Confidentiality
Complete
Integrity
Complete
Availability
Complete

AV:N/AC:L/Au:N/C:C/I:C/A:C

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. Verify if X server is listening on network ports
    Check for X server listening on ports 6000-6063 (common X display ports). Use 'netstat -an | grep 600' or 'ss -tlnp | grep -E "6[0-9]{3}"' on Unix systems.
    Affected if X server is bound to 0.0.0.0 or accessible over network on port 6000+
  2. Confirm MIT-MAGIC-COOKIE-1 is the authentication type
    Run 'xauth list' to display X authentication entries. Look for 'MIT-MAGIC-COOKIE-1' in the output for display entries.
    Affected if MIT-MAGIC-COOKIE-1 is listed as the authentication mechanism for active displays
  3. Check xhost access controls
    Run 'xhost' with no arguments to display current access control list. Look for '+' which indicates unrestricted access from any host.
    Affected if xhost shows '+' or includes untrusted remote hosts in the access list
  4. Inspect X authority file permissions and contents
    Check the .Xauthority file in the user's home directory with 'ls -la ~/.Xauthority'. Examine if cookies are easily readable or if the file has weak permissions (world-readable).
    Affected if The .Xauthority file exists, contains MIT-MAGIC-COOKIE-1 entries, and is readable by other users or processes
  5. Determine if SSH X11 forwarding is in use without encryption
    Check if /etc/ssh/sshd_config contains 'X11Forwarding yes' and review if X connections are going directly over network rather than through SSH tunnel.
    Affected if X11 forwarding is enabled but X server remains network-accessible on native ports

A user is affected if their X server uses MIT-MAGIC-COOKIE-1 authentication and is accessible over the network without restricted xhost controls or SSH tunnel encryption.

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

Restrict X server access using xhost/xauth controls, firewall rules, or SSH X11 forwarding; disable direct X access over network or upgrade to more secure authentication mechanisms like SUN-DES-1 or Kerberos.

Recommended fix Moderate confidence

Modern Linux/Unix distributions with current X11 implementations (X.org X11R7.x or later) that have improved authentication mechanisms

  1. Use SSH X11 forwarding instead of direct X11 connections (ssh -X or ssh -Y) to encrypt and secure X11 traffic
  2. If SSH X11 forwarding is not possible, configure the X server to use MIT-MAGIC-COOKIE-1 and regenerate the cookie using xauth generate :0 .
  3. Alternatively, disable X11 access control entirely with xhost + ONLY if the system is isolated on a trusted network, then re-enable with xhost -
  4. Consider using a different X11 display manager like XDMCP with stronger authentication or moving to a modern desktop environment that uses Wayland
  5. Ensure firewall rules restrict X11 ports (6000-6063) to trusted hosts only
Caveat Modern Wayland-based systems may not be compatible with legacy X11 applications; some older IRIX/Solaris applications may not run on modern systems

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

Fix this in X11r6 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
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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-1999-0241 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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  • Version or environment caveats, and links to real fixes
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