Date: Thu, 20 Nov 2008 03:16:36 +0300 From: Eygene Ryabinkin <rea-sec@...elabs.ru> To: oss-security@...ts.openwall.com, mike@...ysw.com Cc: "Steven M. Christey" <coley@...re.org> Subject: Re: CVE request: CUPS DoS via RSS subscriptions Josh, Mike, *, good day. Wed, Nov 19, 2008 at 03:14:43PM -0500, Josh Bressers wrote: > So from looking at cups 1.3.7 on Fedora 8, here is what I see: > > (gdb) bt > #0 create_subscription (con=0xb88975c0, uri=0xb889ae00) at ipp.c:5858 > #1 0xb7facba7 in cupsdProcessIPPRequest (con=0xb88975c0) at ipp.c:615 > #2 0xb7f88bfc in cupsdReadClient (con=0xb88975c0) at client.c:2253 > #3 0xb7fc0606 in cupsdDoSelect (timeout=1) at select.c:537 > #4 0xb7f98710 in main (argc=1, argv=0xbfdd6194) at main.c:817 > (gdb) list > 5853 else if (printer) > 5854 cupsdLogMessage(CUPSD_LOG_DEBUG, > 5855 "Added subscription %d for printer \"%s\"", > 5856 sub->id, printer->name); > 5857 else > 5858 cupsdLogMessage(CUPSD_LOG_DEBUG, "Added subscription %d for server", > 5859 sub->id); > 5860 > 5861 sub->interval = interval; > 5862 sub->lease = lease; > (gdb) print sub > $1 = (cupsd_subscription_t *) 0x0 > > It would appear to be a NULL pointer dereference. It seems that this call a > few lines above the snippet shown above: > sub = cupsdAddSubscription(mask, printer, job, recipient, 0); > > will return NULL when the hardcoded value of 100 subscriptions is hit. Not really hardcoded -- it is settable with the 'MaxSubscriptions' directive. I had just reproduced the bug with CUPS 1.3.9 at FreeBSD. MaxSubscriptions was set to 3 to ease the PoC. Just repeated invocations of 'lpr -m <somefile>' were crashing cups daemon reproducibly. The attached patch fixes the things for me, but perhaps it needs some more polishing. Will try to take a fresh look at this tomorrow. Mike, please, take a look at this! -- rea View attachment "a" of type "text/plain" (1548 bytes)
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