Mailing List Archive

Final draft / CVE-2011-3192
Thanks for all the help. All fixes included. Below will go out to announce at the top of the hour - unless I see a veto.

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 SetEnvIf or mod_rewrite to detect a large number of ranges and then
either ignore the Range: header or reject the request.

Option 1: (Apache 2.0 and 2.2)

# 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: (Also for Apache 1.3)

# Reject request when more than 5 ranges in the Range: header.
# CVE-2011-3192
#
RewriteEngine on
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+K1Dqc7g@mail.gmail.com%3e

Actions:
========

However there are several immediate options to mitigate this issue until
that time.

1) Use SetEnvIf or mod_rewrite to detect a large number of ranges and then
either ignore the Range: header or reject the request.

Option 1: (Apache 2.0 and 2.2)

# 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: (Also for Apache 1.3)

# Reject request when more than 5 ranges in the Range: header.
# CVE-2011-3192
#
RewriteEngine on
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+K1Dqc7g@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.
Re: Final draft / CVE-2011-3192 [ In reply to ]
I'm seeing Apache 2.0 doesn't accept our RequestHeader syntax due to a
defect, it misinterprets it as a value and fails startup.

If we have the opportunity to amend, I think we need to suggest the
rewrite flavor for Apache 2.0 and earlier, not just 1.3 and earlier.

Also for 1.3, is our RE safe for non-PCRE? And should we reconsider
the "5" for something more liberal?

>   Option 1: (Apache 2.0 and 2.2)
>
>          # 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: (Also for Apache 1.3)
>
>          # Reject request when more than 5 ranges in the Range: header.
>          # CVE-2011-3192
>          #
>          RewriteEngine on
>          RewriteCond %{HTTP:range} !(^bytes=[^,]+(,[^,]+){0,4}$|^$)
>          RewriteRule .* - [F]
Re: Final draft / CVE-2011-3192 [ In reply to ]
That is fine - we can do another update tomorrow, say noon zulu - if we expect that we do not have a proper patch and/or a 2.0.65 / 2.2.20 in the day following.

Weird though - my 2.0.61 and 64 does seem fine. So probably very early 2.0 series.

Dw

On 24 Aug 2011, at 20:40, Eric Covener wrote:

> I'm seeing Apache 2.0 doesn't accept our RequestHeader syntax due to a
> defect, it misinterprets it as a value and fails startup.
>
> If we have the opportunity to amend, I think we need to suggest the
> rewrite flavor for Apache 2.0 and earlier, not just 1.3 and earlier.
>
> Also for 1.3, is our RE safe for non-PCRE? And should we reconsider
> the "5" for something more liberal?
>
>> Option 1: (Apache 2.0 and 2.2)
>>
>> # 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: (Also for Apache 1.3)
>>
>> # Reject request when more than 5 ranges in the Range: header.
>> # CVE-2011-3192
>> #
>> RewriteEngine on
>> RewriteCond %{HTTP:range} !(^bytes=[^,]+(,[^,]+){0,4}$|^$)
>> RewriteRule .* - [F]
>
Re: Final draft / CVE-2011-3192 [ In reply to ]
For Mitigation of Apache Range Header DoS Attack with mod_security, see
also:

http://blog.spiderlabs.com/2011/08/mitigation-of-apache-range-header-dos-attack.html


----- Original Message -----
From: "Dirk-Willem van Gulik" <dirkx@webweaving.org>
Newsgroups: gmane.comp.apache.devel
To: <security@httpd.apache.org>; <dev@httpd.apache.org>
Sent: Wednesday, August 24, 2011 5:34 PM
Subject: Final draft / CVE-2011-3192


Thanks for all the help. All fixes included. Below will go out to announce
at the top of the hour - unless I see a veto.

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 SetEnvIf or mod_rewrite to detect a large number of ranges and then
either ignore the Range: header or reject the request.

Option 1: (Apache 2.0 and 2.2)

# 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: (Also for Apache 1.3)

# Reject request when more than 5 ranges in the Range: header.
# CVE-2011-3192
#
RewriteEngine on
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+K1Dqc7g@mail.gmail.com%3e

Actions:
========

However there are several immediate options to mitigate this issue until
that time.

1) Use SetEnvIf or mod_rewrite to detect a large number of ranges and then
either ignore the Range: header or reject the request.

Option 1: (Apache 2.0 and 2.2)

# 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: (Also for Apache 1.3)

# Reject request when more than 5 ranges in the Range: header.
# CVE-2011-3192
#
RewriteEngine on
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+K1Dqc7g@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.
Re: Final draft / CVE-2011-3192 [ In reply to ]
Thanks. Added to the interim draft update.

Dw.

On 25 Aug 2011, at 06:36, Steffen wrote:

> For Mitigation of Apache Range Header DoS Attack with mod_security, see
> also:
>
> http://blog.spiderlabs.com/2011/08/mitigation-of-apache-range-header-dos-attack.html
>
>
> ----- Original Message -----
> From: "Dirk-Willem van Gulik" <dirkx@webweaving.org>
> Newsgroups: gmane.comp.apache.devel
> To: <security@httpd.apache.org>; <dev@httpd.apache.org>
> Sent: Wednesday, August 24, 2011 5:34 PM
> Subject: Final draft / CVE-2011-3192
>
>
> Thanks for all the help. All fixes included. Below will go out to announce
> at the top of the hour - unless I see a veto.
>
> 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 SetEnvIf or mod_rewrite to detect a large number of ranges and then
> either ignore the Range: header or reject the request.
>
> Option 1: (Apache 2.0 and 2.2)
>
> # 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: (Also for Apache 1.3)
>
> # Reject request when more than 5 ranges in the Range: header.
> # CVE-2011-3192
> #
> RewriteEngine on
> 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+K1Dqc7g@mail.gmail.com%3e
>
> Actions:
> ========
>
> However there are several immediate options to mitigate this issue until
> that time.
>
> 1) Use SetEnvIf or mod_rewrite to detect a large number of ranges and then
> either ignore the Range: header or reject the request.
>
> Option 1: (Apache 2.0 and 2.2)
>
> # 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: (Also for Apache 1.3)
>
> # Reject request when more than 5 ranges in the Range: header.
> # CVE-2011-3192
> #
> RewriteEngine on
> 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+K1Dqc7g@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.
>
>
>
>
>