X.org libXdmcp up to 1.1.2 Session Key XdmcpGenerateKey information disclosure

CVSS Meta Temp Score
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6.1$0-$5k0.00

Summaryinfo

A vulnerability, which was classified as critical, was found in X.org libXdmcp up to 1.1.2. Impacted is the function XdmcpGenerateKey of the component Session Key Handler. The manipulation results in information disclosure. This vulnerability is cataloged as CVE-2017-2624. The attack must be initiated from a local position. There is no exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability classified as critical has been found in X.org libXdmcp up to 1.1.2. Affected is the function XdmcpGenerateKey of the component Session Key Handler. The manipulation with an unknown input leads to a information disclosure vulnerability. CWE is classifying the issue as CWE-200. The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

It was found that xorg-x11-server before 1.19.0 including uses memcmp() to check the received MIT cookie against a series of valid cookies. If the cookie is correct, it is allowed to attach to the Xorg session. Since most memcmp() implementations return after an invalid byte is seen, this causes a time difference between a valid and invalid byte, which could allow an efficient brute force attack.

The bug was discovered 02/28/2017. The weakness was shared 02/28/2017 by Eric Sesterhenn with X41 D-Sec GmbH as Advisory X41-2017-001: Multiple Vulnerabilities in X.org as confirmed mailinglist post (Full-Disclosure). The advisory is shared for download at seclists.org. This vulnerability is traded as CVE-2017-2624 since 12/01/2016. The exploitability is told to be difficult. The attack needs to be approached locally. A authentication is required for exploitation. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1592. The reason for this vulnerability is this part of code: 

void
XdmcpGenerateKey (XdmAuthKeyPtr key)
{
#ifndef HAVE_ARC4RANDOM_BUF
	long    lowbits, highbits;

	void
XdmcpGenerateKey (XdmAuthKeyPtr key)
{
#ifndef HAVE_ARC4RANDOM_BUF
   long    lowbits, highbits;

   srandom ((int)getpid() ^ time((Time_t *)0));
   lowbits = random ();
   highbits = random ();
   getbits (lowbits, key->data);
   getbits (highbits, key->data + 4);
#else
   arc4random_buf(key->data, 8);
#endif
}

The vulnerability scanner Nessus provides a plugin with the ID 101949 (Ubuntu 14.04 LTS / 16.04 LTS / 17.04 : xorg-server, xorg-server-hwe-16.04, xorg-server-lts-xenial vulnerabilities (USN-3362-1)), which helps to determine the existence of the flaw in a target environment. It is assigned to the family Ubuntu Local Security Checks and running in the context l. The commercial vulnerability scanner Qualys is able to test this issue with plugin 196856 (Ubuntu Security Notification for Xorg-server, Xorg-server-hwe-16.04, Xorg-server-lts-xenial Vulnerabilities (USN-3362-1)).

Upgrading eliminates this vulnerability. A possible mitigation has been published 6 months after the disclosure of the vulnerability.

The vulnerability is also documented in the databases at Tenable (101949), SecurityFocus (BID 96480†) and SecurityTracker (ID 1037919†). The entries VDB-97342, VDB-97343, VDB-97345 and VDB-97346 are related to this item. VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔍
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.1
VulDB Meta Temp Score: 6.1

VulDB Base Score: 4.5
VulDB Temp Score: 4.3
VulDB Vector: 🔍
VulDB Reliability: 🔍

Researcher Base Score: 7.1
Researcher Vector: 🔍

NVD Base Score: 7.0
NVD Vector: 🔍

CNA Base Score: 5.9
CNA Vector: 🔍

CVSSv2info

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

NVD Base Score: 🔍

Exploitinginfo

Class: Information disclosure
CWE: CWE-200 / CWE-284 / CWE-266
CAPEC: 🔍
ATT&CK: 🔍

Physical: Partially
Local: Yes
Remote: No

Availability: 🔍
Status: Not defined

EPSS Score: 🔍
EPSS Percentile: 🔍

Price Prediction: 🔍
Current Price Estimation: 🔍

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Nessus ID: 101949
Nessus Name: Ubuntu 14.04 LTS / 16.04 LTS / 17.04 : xorg-server, xorg-server-hwe-16.04, xorg-server-lts-xenial vulnerabilities (USN-3362-1)
Nessus File: 🔍
Nessus Risk: 🔍
Nessus Family: 🔍
Nessus Context: 🔍

OpenVAS ID: 841810
OpenVAS Name: Ubuntu Update for xorg-server USN-3362-1
OpenVAS File: 🔍
OpenVAS Family: 🔍

Qualys ID: 🔍
Qualys Name: 🔍

Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

Reaction Time: 🔍
0-Day Time: 🔍
Exposure Time: 🔍

Timelineinfo

12/01/2016 🔍
02/28/2017 +89 days 🔍
02/28/2017 +0 days 🔍
02/28/2017 +0 days 🔍
02/28/2017 +0 days 🔍
02/28/2017 +0 days 🔍
07/24/2017 +146 days 🔍
07/25/2017 +1 days 🔍
07/27/2018 +367 days 🔍
08/29/2025 +2590 days 🔍

Sourcesinfo

Vendor: x.org

Advisory: Advisory X41-2017-001: Multiple Vulnerabilities in X.org
Researcher: Eric Sesterhenn
Organization: X41 D-Sec GmbH
Status: Confirmed
Confirmation: 🔍

CVE: CVE-2017-2624 (🔍)
GCVE (CVE): GCVE-0-2017-2624
GCVE (VulDB): GCVE-100-97344
SecurityFocus: 96480 - X.org X Server Local Multiple Security Vulnerabilities
OSVDB: - CVE-2017-2624 - xorg-x11-server - Brute Force Issue
SecurityTracker: 1037919

See also: 🔍

Entryinfo

Created: 02/28/2017 20:24
Updated: 08/29/2025 16:56
Changes: 02/28/2017 20:24 (82), 08/18/2020 07:14 (17), 08/29/2025 16:56 (29)
Complete: 🔍
Cache ID: 216::103

VulDB is the best source for vulnerability data and more expert information about this specific topic.

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