With the current fixes, +1 On Aug 24, 2011, at 10:56 AM, Dirk-Willem van Gulik wrote:
> Various suggest on-list and off-list fixes applied. Thanks all. > > A few more +1's would be nice :) > > Dw. > > > > > > Title: CVE-2011-3192: Range header DoS vulnerability Apache HTTPD 1.3/2.x > Apache HTTPD Security ADVISORY > > Date: 20110824 1600Z > Product: Apache HTTPD Web Server > Versions: Apache 1.3 all versions, Apache 2 all versions > > Description: > ------------ > > A denial of service vulnerability has been found in the way the multiple > overlapping ranges are handled by the Apache HTTPD server: > > http://seclists.org/fulldisclosure/2011/Aug/175 > > An attack tool is circulating in the wild. Active use of this tools has been > observed. > > The attack can be done remotely and with a modest number of requests can > cause very significant memory and CPU usage on the server. > > The default Apache HTTPD installation is vulnerable. > > There is currently no patch/new version of Apache HTTPD which fixes this > vulnerability. This advisory will be updated when a long term fix is > available. > > A full fix is expected in the next 48 hours. > > Mitigation: > ------------ > > However there are several immediate options to mitigate this issue until that > time. > > 1) Use mod_rewrite to limit the number of ranges: > > Option 1: > # drop Range header when more than 5 ranges. > # CVE-2011-3192 > SetEnvIf Range (,.*?){5,} bad-range=1 > RequestHeader unset Range env=bad-range > > # optional logging. > CustomLog logs/range-CVE-2011-3192.log common env=bad-range > > Option 2: > # Reject request when more than 5 ranges in the Range: header. > # CVE-2011-3192 > # > RewriteCond %{HTTP:range} !(^bytes=[^,]+(,[^,]+){0,4}$|^$) > RewriteRule .* - [F] > > The number 5 is arbitrary. Several 10's should not be an issue and may be > required for sites which for example serve PDFs to very high end eReaders > or use things such complex http based video streaming. > > 2) Limit the size of the request field to a few hundred bytes. Note that > while this > keeps the offending Range header short - it may break other headers; such > as > sizeable cookies or security fields. > > LimitRequestFieldSize 200 > > Note that as the attack evolves in the field you are likely to have > to further limit this and/or impose other LimitRequestFields limits. > > See: http://httpd.apache.org/docs/2.2/mod/core.html#limitrequestfieldsize > > 3) Use mod_headers to completely dis-allow the use of Range headers: > > RequestHeader unset Range > > Note that this may break certain clients - such as those used for > e-Readers and progressive/http-streaming video. > > 4) Deploy a Range header count module as a temporary stopgap measure: > > http://people.apache.org/~dirkx/mod_rangecnt.c > > Precompiled binaries for some platforms are available at: > > http://people.apache.org/~dirkx/BINARIES.txt > > 5) Apply any of the current patches under discussion - such as: > > > http://mail-archives.apache.org/mod_mbox/httpd-dev/201108.mbox/%3ccaapsnn2po-d-c4nqt_tes2rrwizr7urefhtkpwbc1b+k1dq...@mail.gmail.com%3e > > Actions: > ----------- > Apache HTTPD users who are concerned about a DoS attack against their server > should consider implementing any of the above mitigations immediately. > > When using a third party attack tool to verify vulnerability - know that most > of the versions in the wild currently check for the presence of mod_deflate; > and will (mis)report that your server is not vulnerable if this module is not > present. This vulnerability is not dependent on presence or absence of that > module. > > Planning: > ------------- > This advisory will be updated when new information, a patch or a new release > is available. A patch or new apache release for Apache 2.0 and 2.2 is > expected in the next 48 hours. Note that, while popular, Apache 1.3 is > deprecated. >
