X.org X11 Server Access Control improper authentication

CVSS Meta Temp Score
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Current Exploit Price (≈)
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CTI Interest Score
Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
9.4$0-$5k0.00

Summaryinfo

A vulnerability, which was classified as critical, has been found in X.org X11 Server. Impacted is an unknown function of the component Access Control Handler. The manipulation leads to improper authentication. This vulnerability is documented as CVE-1999-0526. Additionally, an exploit exists. This vulnerability is considered historic because of its background and reception. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in X.org X11 Server (Windowing System Software) (affected version unknown). It has been rated as very critical. This issue affects an unknown functionality of the component Access Control Handler. The manipulation with an unknown input leads to a improper authentication vulnerability. Using CWE to declare the problem leads to CWE-287. When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

An X server's access control is disabled (e.g. through an "xhost +" command) and allows anyone to connect to the server.

The weakness was released 07/01/1997 as VU#704969 as confirmed advisory (CERT.org). It is possible to read the advisory at kb.cert.org. The identification of this vulnerability is CVE-1999-0526. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are unknown but a public exploit is available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 04/16/2026). Due to its background and reception, this vulnerability has a historic impact.

It is declared as highly functional. The vulnerability scanner Nessus provides a plugin with the ID 19948 (X11 Server Unauthenticated Access), which helps to determine the existence of the flaw in a target environment. It is assigned to the family Misc. and running in the context r. The commercial vulnerability scanner Qualys is able to test this issue with plugin 95001 (X-Window Sniffing).

Upgrading eliminates this vulnerability.

The vulnerability is also documented in the databases at X-Force (155), Tenable (19948), OSVDB (309†) and Vulnerability Center (SBV-17†). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Type

Vendor

Name

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔍
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 9.8
VulDB Meta Temp Score: 9.4

VulDB Base Score: 9.8
VulDB Temp Score: 9.4
VulDB Vector: 🔍
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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💳💳💳💳💳💳
💳💳💳💳💳💳
VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔍
VulDB Temp Score: 🔍
VulDB Reliability: 🔍

NVD Base Score: 🔍

Exploitinginfo

Class: Improper authentication
CWE: CWE-287
CAPEC: 🔍
ATT&CK: 🔍

Physical: No
Local: No
Remote: Yes

Availability: 🔍
Access: Public
Status: Highly functional

EPSS Score: 🔍
EPSS Percentile: 🔍

Price Prediction: 🔍
Current Price Estimation: 🔍

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Nessus ID: 19948
Nessus Name: X11 Server Unauthenticated Access
Nessus File: 🔍
Nessus Risk: 🔍
Nessus Family: 🔍
Nessus Context: 🔍

OpenVAS ID: 15897
OpenVAS Name: Open X Server
OpenVAS File: 🔍
OpenVAS Family: 🔍

Qualys ID: 🔍
Qualys Name: 🔍

MetaSploit ID: open_x11.rb
MetaSploit Name: WinRM WQL Query Runner
MetaSploit File: 🔍

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔍

Timelineinfo

07/01/1997 🔍
07/01/1997 +0 days 🔍
07/01/1997 +0 days 🔍
09/12/2002 +1899 days 🔍
10/08/2002 +25 days 🔍
10/10/2005 +1098 days 🔍
06/18/2014 +3173 days 🔍
04/16/2026 +4320 days 🔍

Sourcesinfo

Vendor: x.org

Advisory: VU#704969
Status: Confirmed

CVE: CVE-1999-0526 (🔍)
GCVE (CVE): GCVE-0-1999-0526
GCVE (VulDB): GCVE-100-13931
CERT: 🔍
X-Force: 155
OSVDB: 309 - Multiple Vendor X Server Unauthenticated Access
Vulnerability Center: 17 - Xhost Session Hijacking, Low

scip Labs: https://www.scip.ch/en/?labs.20161013

Entryinfo

Created: 06/18/2014 12:05
Updated: 04/16/2026 21:04
Changes: 06/18/2014 12:05 (74), 05/04/2019 16:40 (1), 06/07/2024 11:56 (17), 04/23/2025 00:59 (3), 10/25/2025 23:12 (2), 04/16/2026 21:04 (1)
Complete: 🔍
Cache ID: 216::103

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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