Date: Fri, 3 Oct 2014 13:53:02 +0200 From: Rainer Gerhards <rgerhards@...adiscon.com> To: Solar Designer <solar@...nwall.com> Cc: Martin Schulze <joey@...odrom.org>, oss-security@...ts.openwall.com Subject: Re: sysklogd vulnerability (CVE-2014-3634) Sent from phone, thus brief. Am 03.10.2014 13:26 schrieb "Solar Designer" <solar@...nwall.com>: > > On Fri, Oct 03, 2014 at 11:24:43AM +0000, mancha wrote: > > On Fri, Oct 03, 2014 at 09:12:28AM +0000, mancha wrote: > > > In sysklogd's syslogd, invalid priority values between 192 and 1023 > > > (directly or arrived at via overflow wraparound) can propagate through > > > code causing out-of-bounds access to the f_pmask array within the > > > 'filed' structure by up to 104 bytes past its end. Though most likely > > > insufficient to reach unallocated memory because there are around 544 > > > bytes past f_pmask in 'filed' (mod packing and other differences), > > > incorrect access of fields at higher positions of the 'filed' > > > structure definition can cause unexpected behavior including message > > > mis-classification, forwarding issues, message loss, or other. > > > > To expand on the above, because the out-of-bounds access is limited to > > the filed structure, the effect on message handling, etc. appears > > limited to the would-be attacker's own message. Unlike the more serious > > impact seen in rsyslog, my limited testing and code review suggests the > > flaw, while there, has no real security impact. Nevertheless, my patch > > fixes the handling of malformed PRI parts. > > What about the DoS impact claimed here, though? - > > http://www.rsyslog.com/remote-syslog-pri-vulnerability-cve-2014-3683/ > > sysklogd > ~~~~~~~~ > A segfault seems possible in sysklogd if a negative facility value (due to > integer overrun in facility parsing) is used. This could be used to > carry out a remote DoS. > > If this can be used to crash syslogd, it's "real security impact", even > if rather limited. > > Have you tried triggering this condition (getting syslogd to crash)? I didn't try out sysklogd as I was busy enough with rsyslog BUT I can crash unpatched rsyslog v3 and the code path in question is extremely similar in those two. Note that a carefully crafted overflow pri may lead to a 2gb misadressing below f_pmask, which most probably is outside of the address space. I haven't checked, though, if i can craft such a pri. But you have around 1000 digits for trying, so I think its possible. Mancha may have more concrete information. Rainer > > Alexander
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