Date: Wed, 19 Nov 2008 17:54:49 -0800 From: Michael Sweet <mike@...ysw.com> To: Eygene Ryabinkin <rea-sec@...elabs.ru> CC: oss-security@...ts.openwall.com, "Steven M. Christey" <coley@...re.org> Subject: Re: CVE request: CUPS DoS via RSS subscriptions Eygene Ryabinkin wrote: > 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! You'll find a much more complete patch already in CUPS svn for both 1.3.x and 1.4.x, along with a new subscription test for the "make check" target. I didn't withhold the patch since the browser attack vector was closed in 1.3.8... I've attached my 1.3.x patch... -- ______________________________________________________________________ Michael Sweet, Easy Software Products mike at easysw dot com View attachment "cups-1.3-max-subscriptions.patch" of type "text/plain" (5341 bytes)
Powered by blists - more mailing lists
Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.