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

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.
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{
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    "category": "csaf_security_advisory",
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    "distribution": {
      "text": "Copyright \u00a9 Red Hat, Inc. All rights reserved.",
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    "lang": "en",
    "notes": [
      {
        "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.",
        "title": "Topic"
      },
      {
        "category": "general",
        "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.",
        "title": "Details"
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      {
        "category": "legal_disclaimer",
        "text": "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.",
        "title": "Terms of Use"
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        "url": "https://security.access.redhat.com/data/csaf/v2/advisories/2003/rhsa-2003_041.json"
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    "title": "Red Hat Security Advisory: : : : Updated VNC packages fix replay and cookie vulnerabilities",
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      "id": "RHSA-2003:041",
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      "revision_history": [
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          "date": "2003-02-21T08:40:00+00:00",
          "number": "1",
          "summary": "Initial version"
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      "notes": [
        {
          "category": "description",
          "text": "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.",
          "title": "Vulnerability description"
        },
        {
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        {
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      "release_date": "2002-07-26T00:00:00+00:00",
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          "date": "2003-02-21T08:40:00+00:00",
          "details": "Before applying this update, make sure all previously released errata\nrelevant to your system have been applied.\n\nTo update all RPMs for your particular architecture, run:\n\nrpm -Fvh [filenames]\n\nwhere [filenames] is a list of the RPMs you wish to upgrade.  Only those\nRPMs which are currently installed will be updated.  Those RPMs which are\nnot installed but included in the list will not be updated.  Note that you\ncan also use wildcards (*.rpm) if your current directory *only* contains the\ndesired RPMs.\n\nPlease note that this update is also available via Red Hat Network.  Many\npeople find this an easier way to apply updates.  To use Red Hat Network,\nlaunch the Red Hat Update Agent with the following command:\n\nup2date\n\nThis will start an interactive process that will result in the appropriate\nRPMs being upgraded on your system.",
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        {
          "category": "description",
          "text": "The vncserver wrapper for vnc before 3.3.3r2-21 uses the rand() function instead of srand(), which causes vncserver to generate weak cookies.",
          "title": "Vulnerability description"
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      "release_date": "2002-10-11T00:00:00+00:00",
      "remediations": [
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          "date": "2003-02-21T08:40:00+00:00",
          "details": "Before applying this update, make sure all previously released errata\nrelevant to your system have been applied.\n\nTo update all RPMs for your particular architecture, run:\n\nrpm -Fvh [filenames]\n\nwhere [filenames] is a list of the RPMs you wish to upgrade.  Only those\nRPMs which are currently installed will be updated.  Those RPMs which are\nnot installed but included in the list will not be updated.  Note that you\ncan also use wildcards (*.rpm) if your current directory *only* contains the\ndesired RPMs.\n\nPlease note that this update is also available via Red Hat Network.  Many\npeople find this an easier way to apply updates.  To use Red Hat Network,\nlaunch the Red Hat Update Agent with the following command:\n\nup2date\n\nThis will start an interactive process that will result in the appropriate\nRPMs being upgraded on your system.",
          "product_ids": [
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            "Red Hat Linux 7.2",
            "Red Hat Linux 7.3",
            "Red Hat Linux 8.0"
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      "threats": [
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          "category": "impact",
          "details": "Moderate"
        }
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      "title": "security flaw"
    }
  ]
}


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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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