dbcve.org
X11Application · X.org

CVE-1999-0526

HIGH · 10.0 CVSS v2.0 Published 1997-07-01
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
An X server's access control is disabled (e.g. through an "xhost +" command) and allows anyone to connect to the server.

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

The X Window System server has its access control mechanism disabled, typically through execution of the 'xhost +' command, which removes all host-based authentication restrictions. This allows any remote or local user to connect to the X server without authentication, enabling viewing of displayed content, keystroke interception, and potential session hijacking.

MitigationImmediately remove the insecure 'xhost +' configuration and restore X server access control. Use xauth with MIT-MAGIC-COOKIE-1 for secure authentication, or implement TCP wrapper restrictions if remote X connections are necessary.

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
X11Application
Affected:= 7.1_1.1.0

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. Check xhost access control list
    Run 'xhost' command and examine the output. Look specifically for a '+' character alone on a line, which indicates all hosts have access.
    Affected if The output contains '+' or shows no access restrictions, meaning anyone can connect to the X server.
  2. Verify X server TCP listening status
    Run 'netstat -an | grep 600' or 'ss -tlnp | grep 600' to check if the X server is listening on TCP port 6000 (or higher for multiple displays).
    Affected if The X server is listening on TCP ports, making it network-accessible without authentication.
  3. Inspect startup scripts for xhost +
    Search for 'xhost +' in shell initialization files such as ~/.bashrc, ~/.profile, /etc/profile, and ~/.Xsession or /etc/X11/xdm/Xsession. Use grep to search: 'grep -r "xhost +" ~/. /etc/'
    Affected if The 'xhost +' command is found in any startup or configuration file, indicating the insecure setting is applied on boot.
  4. Check DISPLAY environment variable configuration
    Run 'echo $DISPLAY' to see how the display is configured. A value like ':0' or '*:0' typically indicates TCP listening, while ':0' with Unix socket uses local-only access.
    Affected if The DISPLAY variable shows the X server is configured for TCP connections rather than Unix sockets.

If 'xhost' shows '+' in its output, the X server has TCP listeners, or startup scripts contain 'xhost +', then the system is vulnerable to unauthenticated X connections.

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

Immediately remove the insecure 'xhost +' configuration and restore X server access control. Use xauth with MIT-MAGIC-COOKIE-1 for secure authentication, or implement TCP wrapper restrictions if remote X connections are necessary.

Recommended fix High confidence
  1. Remove any 'xhost +' commands from startup scripts (/etc/init.d/, ~/.xinitrc, ~/.xsession, /etc/X11/xinit/xinitrc, or similar)
  2. If xhost + was run manually, run 'xhost -' to re-enable access control
  3. Configure X server to use proper authentication by ensuring XAUTHORITY environment variable is set and xauth is being used
  4. For remote X connections, use SSH with X11 forwarding (-X or -Y flag) instead of direct network access
  5. If direct X access over network is required, use 'xhost +hostname' to add specific trusted hosts rather than disabling access control entirely
  6. Consider using X servers that support modern authentication mechanisms like MIT-MAGIC-COOKIE-1 or SUN-DES-1

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

Fix this in X11 Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
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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-1999-0526 in production — separate from our analysis above.

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