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PHP: integer overflow of dechunk
Synthesis of the vulnerability
An attacker can generate an integer overflow in the PHP filter reassembling HTTP chunk encoded data.
Vulnerable systems: openSUSE, PHP, SLES.
Severity of this threat: 2/4.
Consequences of a hack: denial of service on service.
Pirate's origin: intranet server.
Creation date: 04/05/2010.
Références of this weakness: BID-39877, CVE-2010-1866, MOPS-2010-003, openSUSE-SU-2010:0599-1, openSUSE-SU-2010:0678-1, SUSE-SR:2010:017, VIGILANCE-VUL-9626.
Description of the vulnerability
An HTTP response can be split in several "chunks", by using the "Transfer-Encoding: chunked" header.
The PHP file_get_contents() function can use filters to manage data. The "read=dechunk" filter automatically reassembles HTTP fragments.
However, this filter does not correctly manage negative chunk sizes, which corrupts the memory.
An attacker with a malicious HTTP server can therefore send a malicious reply to PHP applications using this filter. This error leads to a denial of service, and eventually to code execution.
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