[Full-Disclosure] iDEFENSE Security Advisory 02.21.05: Multiple Unix/Linux Vendor cURL/libcURL NTLM Authentication Buffer Overflow Vulnerability

idlabs-advisories_at_idefense.com
Date: 02/21/05

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    Date: Mon, 21 Feb 2005 15:28:41 -0500
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    Multiple Unix/Linux Vendor cURL/libcURL NTLM Authentication Buffer
    Overflow Vulnerability

    iDEFENSE Security Advisory 02.21.05:
    www.idefense.com/application/poi/display?id=202&type=vulnerabilities
    February 21, 2005

    I. BACKGROUND

    cURL is a command line tool for transferring files with URL syntax,
    supporting FTP, FTPS, HTTP, HTTPS, GOPHER, TELNET, DICT, FILE and LDAP.
    More information about cURL and libcURL is available from:

        http://curl.haxx.se/

    II. DESCRIPTION

    Remote exploitation of a stack-based buffer overflow in various Unix /
    Linux vendors implementations of cURL could allow for arbitrary code
    execution on the targeted host.

    An exploitable stack-based buffer overflow condition exists when using
    NT Lan Manager (NTLM) authentication. The problem specifically exists
    within Curl_input_ntlm() defined in lib/http_ntlm.c. Within this
    function an unsigned stack-based character array of size 256, buffer[],
    is passed to the Curl_base64_decode() routine defined in lib/base64.c as
    can be seen here:

        size_t size = Curl_base64_decode(header, (char *)buffer);

    The Curl_base64_decode() routine relies on the calling function to
    validate the decoded length. This function base64 decodes and copies
    data directly from the HTTP reply of a server to the destination buffer,
    in this case buffer[]. An attacker can construct a long base64 encoded
    malicious payload that upon decoding will overflow the 256 byte static
    buffer and overwrite the saved EIP. This in turn can lead to arbitrary
    code execution.

    III. ANALYSIS

    Successful exploitation allows remote attackers to execute arbitrary
    code
    under the privileges of the target user. Exploitation requires that an
    attacker either coerce or force a target to connect to a malicious
    server using NTLM authentication.

    IV. DETECTION

    iDEFENSE has confirmed the existence of this vulnerability in cURL
    version 7.12.1. It is suspected that prior versions are affected as
    well.
    Any application built using a vulnerable version libcURL will also be
    affected.

    V. WORKAROUND

    Replace the static buffer allocation on line 106 in lib/http_ntlm.c:

        unsigned char buffer[256];

    With a dynamic buffer allocation:

        unsigned char *buffer = (unsigned char *)malloc(strlen(header));

    and recompile cURL.

    VI. VENDOR RESPONSE

    No vendor response received.

    VII. CVE INFORMATION

    A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not
    been assigned yet.

    VIII. DISCLOSURE TIMELINE

    12/21/2004 Initial vendor notification - No response
    02/10/2005 Secondary vendor notification - No response
    02/21/2005 Public disclosure

    IX. CREDIT

    infamous41md[at]hotpop.com is credited with this discovery.

    Get paid for vulnerability research
    http://www.idefense.com/poi/teams/vcp.jsp

    X. LEGAL NOTICES

    Copyright (c) 2005 iDEFENSE, Inc.

    Permission is granted for the redistribution of this alert
    electronically. It may not be edited in any way without the express
    written consent of iDEFENSE. If you wish to reprint the whole or any
    part of this alert in any other medium other than electronically, please
    email customerservice@idefense.com for permission.

    Disclaimer: The information in the advisory is believed to be accurate
    at the time of publishing based on currently available information. Use
    of the information constitutes acceptance for use in an AS IS condition.
    There are no warranties with regard to this information. Neither the
    author nor the publisher accepts any liability for any direct, indirect,
    or consequential loss or damage arising from use of, or reliance on,
    this information.

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