BugTraq
[PRE-SA-2012-02] Incorrect loop construct and numeric overflow in libzip Mar 27 2012 07:34AM
Timo Warns (Warns Pre-Sense DE)
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 (at) pre-secure (dot) de. [email concealed] For PGP key
information, refer to http://www.pre-cert.de/.

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