PHP 4 zip_entry_read() Integer Overflow Vulnerability

Credit: Stefan Esser
Risk: Medium
Local: Yes
Remote: No

The zip_read_entry() function that is used to read the content of a file stored inside a .ZIP archive is vulnerable to an integer overflow in memory allocation that leads to an exploitable bufferoverflow. The zip_read_entry() function does not perform any check on the supplied length parameter. Therefore an integer overflow in memory allocation can happen when it adds one byte for a terminating ASCIIZ character. buf = emalloc(len + 1); ret = zzip_read(entry->fp, buf, len); buf[ret] = 0; When a length of 0xffffffff is supplied the allocated memory block will be of size 0 while up to 4 GB of data is read from the ZIP archive into this memory block. This will overwrite everything behind the allocated block and can lead to the execution of arbitrary code. Proof of concept, exploit or instructions to reproduce The attached exploit consists of a small PHP POC and the supplied ZIP archive that contains the data that will overflow the buffer. Because this bug is just a standard heap overflow the POC only shows the crash inside the unlink macro. $ gdb ./php (...) (gdb) run MOPB-35-2007.php Starting program: /../php-4.4.4/sapi/cli/php MOPB-35-2007.php Program received signal SIGSEGV, Segmentation fault. 0x0812c127 in _efree (ptr=0x81d76ec) at /../php-4.4.4/Zend/zend_alloc.c:274 274 REMOVE_POINTER_FROM_LIST(p); (gdb) x/5i $eip 0x812c127 <_efree+71>: mov %eax,(%edx) 0x812c129 <_efree+73>: mov (%ebx),%edx 0x812c12b <_efree+75>: test %edx,%edx 0x812c12d <_efree+77>: je 0x812c135 <_efree+85> 0x812c12f <_efree+79>: mov 0x4(%ebx),%eax (gdb) i r eax 0x44444444 1145324612 ecx 0x8c8c8c9 147376329 edx 0x45454545 1162167621 ebx 0x81d76e0 136148704 esp 0xbff3ae20 0xbff3ae20 ebp 0xbff3ae28 0xbff3ae28 esi 0x81d265c 136128092 edi 0x81d71b4 136147380 eip 0x812c127 0x812c127 <_efree+71> eflags 0x10216 66070 cs 0x73 115 ss 0x7b 123 ds 0x7b 123 es 0x7b 123 fs 0x0 0 gs 0x33 51 (gdb) Notes Nothing special, just a normal heap overflow. SecurityReason Note : Exploit -

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