RHSA-2003:041

Vulnerability from csaf_redhat - Published: 2003-02-21 08:40 - Updated: 2025-11-21 17:25
Summary
Red Hat Security Advisory: : : : Updated VNC packages fix replay and cookie vulnerabilities
Severity
Moderate
Notes
Topic: Updated VNC packages are available, fixing a challenge replay and a weak cookie vulnerability. [Updated 10 July 2003] Added packages for Red Hat Linux on IBM iSeries and pSeries systems.
Details: VNC is a tool for providing a remote graphical user interface. Two vulnerabilities have been found in versions of VNC shipped by Red Hat. The VNC server acts as an X server, but the script for starting it generates an MIT X cookie (which is used for X authentication) without using a sufficiently strong random number generator. This could allow an attacker to more easily guess the authentication cookie. The VNC DES authentication scheme is implemented using a challenge-response architecture, producing a random and different challenge for each authentication attempt. A bug in the function for generating the random challenge caused the random seed to be reset to the current time on every authentication attempt. Therefore, two authentication attempts within the same second could receive the same challenge. An eavesdropper could exploit this vulnerability by replaying the response, thereby gaining authentication. All users of VNC are advised to upgrade to these erratum packages, which contain patches to correct these issues. Note that when using VNC on an untrusted network, always make sure to tunnel it through a secure authenticated protocol such as SSH.
Terms of Use: This content is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). If you distribute this content, or a modified version of it, you must provide attribution to Red Hat Inc. and provide a link to the original.
CVE-2002-1336

TightVNC before 1.2.6 generates the same challenge string for multiple connections, which allows remote attackers to bypass VNC authentication by sniffing the challenge and response of other users.

Affected products
Product Identifier Version Remediation
Red Hat Linux 7.0
Red Hat / Red Hat Linux
 cpe:/o:redhat:linux:7.0 —
Vendor Fix fix
Red Hat Linux 7.1
Red Hat / Red Hat Linux
 cpe:/o:redhat:linux:7.1 —
Vendor Fix fix
Red Hat Linux 7.2
Red Hat / Red Hat Linux
 cpe:/o:redhat:linux:7.2 —
Vendor Fix fix
Red Hat Linux 7.3
Red Hat / Red Hat Linux
 cpe:/o:redhat:linux:7.3 —
Vendor Fix fix
Red Hat Linux 8.0
Red Hat / Red Hat Linux
 cpe:/o:redhat:linux:8.0 —
Vendor Fix fix
Threats
Impact Moderate
CVE-2002-1511

The vncserver wrapper for vnc before 3.3.3r2-21 uses the rand() function instead of srand(), which causes vncserver to generate weak cookies.

Affected products
Fixed 5 products, the same list as for CVE-2002-1336
Threats
Impact Moderate
References
To clipboard 

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        "category": "summary",
        "text": "Updated VNC packages are available, fixing a challenge replay and a weak\ncookie vulnerability.\n\n[Updated 10 July 2003]\nAdded packages for Red Hat Linux on IBM iSeries and pSeries systems.",
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        "text": "VNC is a tool for providing a remote graphical user interface.  Two\nvulnerabilities have been found in versions of VNC shipped by Red Hat.\n\nThe VNC server acts as an X server, but the script for starting it\ngenerates an MIT X cookie (which is used for X authentication) without\nusing a sufficiently strong random number generator.  This could allow an\nattacker to more easily guess the authentication cookie.\n\nThe VNC DES authentication scheme is implemented using a challenge-response\narchitecture, producing a random and different challenge for each\nauthentication attempt. A bug in the function for generating the random\nchallenge caused the random seed to be reset to the current time on every\nauthentication attempt. Therefore, two authentication attempts within the\nsame second could receive the same challenge.  An eavesdropper could\nexploit this vulnerability by replaying the response, thereby gaining\nauthentication.\n\nAll users of VNC are advised to upgrade to these erratum packages, which\ncontain patches to correct these issues.\n\nNote that when using VNC on an untrusted network, always make sure to\ntunnel it through a secure authenticated protocol such as SSH.",
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}



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