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[PRE-SA-2012-02] Incorrect loop construct and numeric overflow in libzip
From: Timo Warns <Warns () Pre-Sense DE>
Date: Tue, 27 Mar 2012 09:34:38 +0200

PRE-CERT Security Advisory
==========================

* Advisory: PRE-SA-2012-02
* Released on: 21st March 2012
* Affected products: libzip <= 0.10
                     PHP 5.4.0
                     PHP <= 5.3.10
                     zipruby <= 0.3.6
* Impact: heap overflow, information leak
* Credit: - Thomas Klausner
          - Timo Warns (PRESENSE Technologies GmbH)
* CVE Identifier: - CVE-2012-1162
                  - CVE-2012-1163


Summary
-------

libzip (version <= 0.10) has two vulnerabilities that may lead to a heap
overflow or an information leak via corrupted zip files. PHP (versions
5.4.0 and <= 5.3.10) and the Ruby binding zipruby (version <= 0.3.6) are
also affected as they include copies of affected libzip versions.

* CVE-2012-1162

    libzip (version <= 0.10) uses an incorrect loop construct, which can
    result in a heap overflow on corrupted zip files.
    
    On opening a zip file with zip_open, libzip reads in the number of
    directory entries in the function _zip_readcdir in zip_open.c:

    (192)    /* number of cdir-entries */
    (193)    nentry = _zip_read2(&cdp);

    Subsequently, memory for directory entries is allocated via
    _zip_cdir_new (in zip_dirent.c) based on the number of directory
    entries:

    (104)    if ((cd->entry=(struct zip_dirent *)malloc(sizeof(*(cd->entry))*nentry))

    If the number of directories in the zip file is set to 0, 0 bytes of
    memory are allocated.

    _zip_readcdir finishes with reading in the directory entries in
    a posttest do-while loop:

    (260)    do {
    (261)        if ((_zip_dirent_read(cd->entry+i, fp, bufp, &left, 0, error)) < 0) {
             ...
    (277)    } while (i<cd->nentry && left > 0);

    If cd->entry points to 0 bytes of allocated memory, _zip_dirent
    writes beyond the allocated memory.

* CVE-2012-1163

    libzip (version <= 0.10) has a numeric overflow condition, which,
    for example, results in improper restrictions of operations within
    the bounds of a memory buffer (e.g., allowing information leaks).

    On opening a zip file with zip_open, libzip reads in the size and the
    offset of the central directory structure in the function _zip_readcdir
    in zip_open.c:

    (198)    cd->size = _zip_read4(&cdp);
    (199)    cd->offset = _zip_read4(&cdp);

    libzip performs a consistency check on these values, but does not
    anticipate an integer overflow:

    (203)    if (cd->offset+cd->size > buf_offset + (eocd-buf)) {

    On an integer overflow, libzip continues to handle the zip file, which,
    for example, can result in improper restriction of operations within the
    bounds of a memory buffer.


Solution
--------

The issue was fixed in the following versions:
    
    libzip 0.10.1

The issue was not fixed in PHP and zipruby yet.


References
----------

When further information becomes available, this advisory will be
updated. The most recent version of this advisory is available at:

http://www.pre-cert.de/advisories/PRE-SA-2012-02.txt


Contact
--------

PRE-CERT can be reached under precert () pre-secure de  For PGP key
information, refer to http://www.pre-cert.de/.

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