Archive for the ‘security’ Category

Unban IP from fail2ban

December 28, 2015

First find the name of the jail using

fail2ban-client statusĀ 

Then remove the IP by entering

fail2ban-client set Jail-nameĀ unbanip


fail2ban-client set ssh unbanip

Linux Kernel “vmsplice()” System Call Vulnerabilities

February 12, 2008

Subject: [SA28835] Linux Kernel “vmsplice()” System Call Vulnerabilities
Date: Tuesday 12 February 2008
From: Secunia Security Advisories

Linux Kernel “vmsplice()” System Call Vulnerabilities



Less critical

Exposure of sensitive information, Privilege escalation, DoS

Local system

Linux Kernel 2.6.x

Some vulnerabilities have been reported in the Linux Kernel, which
can be exploited by malicious, local users to cause a DoS (Denial of
Service), disclose potentially sensitive information, and gain
escalated privileges.

The vulnerabilities are caused due to the missing verification of
parameters within the “vmsplice_to_user()”,
“copy_from_user_mmap_sem()”, and “get_iovec_page_array()” functions
in fs/splice.c before using them to perform certain memory
operations. This can be exploited to e.g. read or write to arbitrary
kernel memory via a specially crafted “vmsplice()” system call.

Successful exploitation allows attackers to e.g. gain “root”

Note: The affected system call first appeared in version 2.6.17.

Update to version or

Wojciech Purczynskiof iSEC Security Research and qaaz

iSEC Security Research:



This Advisory was delivered by Secunia as a free service to help
everybody keeping their systems up to date against the latest


Definitions: (Criticality, Where etc.)

Please Note:
Secunia recommends that you verify all advisories you receive by
clicking the link.
Secunia NEVER sends attached files with advisories.
Secunia does not advise people to install third party patches, only
use those supplied by the vendor.



September 4, 2007

Mod_evasive is an evasive maneuvers module for Apache to provide evasive
action in the event of an HTTP DoS or DDoS attack or brute force attack. It
is also designed to be a detection tool, and can be easily configured to talk
to ipchains, firewalls, routers, and etcetera.

Detection is performed by creating an internal dynamic hash table of IP
Addresses and URIs, and denying any single IP address from any of the following:

– Requesting the same page more than a few times per second
– Making more than 50 concurrent requests on the same child per second
– Making any requests while temporarily blacklisted (on a blocking list)

This method has worked well in both single-server script attacks as well
as distributed attacks, but just like other evasive tools, is only as
useful to the point of bandwidth and processor consumption (e.g. the
amount of bandwidth and processor required to receive/process/respond
to invalid requests), which is why it’s a good idea to integrate this
with your firewalls and routers.

This module instantiates for each listener individually, and therefore has
a built-in cleanup mechanism and scaling capabilities. Because of this,
legitimate requests are rarely ever compromised, only legitimate attacks. Even
a user repeatedly clicking on ‘reload’ should not be affected unless they do
it maliciously.



A web hit request comes in. The following steps take place:

– The IP address of the requestor is looked up on the temporary blacklist
– The IP address of the requestor and the URI are both hashed into a “key”.
A lookup is performed in the listener’s internal hash table to determine
if the same host has requested this page more than once within the past
1 second.
– The IP address of the requestor is hashed into a “key”.
A lookup is performed in the listerner’s internal hash table to determine
if the same host has requested more than 50 objects within the past
second (from the same child).

If any of the above are true, a 403 response is sent. This conserves
bandwidth and system resources in the event of a DoS attack. Additionally,
a system command and/or an email notification can also be triggered to block
all the originating addresses of a DDoS attack.




Without DSO Support:

1. Extract this archive into src/modules in the Apache source tree

2. Run ./configure –add-module=src/modules/evasive/mod_evasive.c

3. make, install

4. Restart Apache

With DSO Support, Ensim, or CPanel:

1. $APACHE_ROOT/bin/apxs -iac mod_evasive.c

2. Restart Apache



mod_evasive has default options configured, but you may also add the
following block to your httpd.conf:


DOSHashTableSize 3097
DOSPageCount 2
DOSSiteCount 50
DOSPageInterval 1
DOSSiteInterval 1
DOSBlockingPeriod 10


DOSHashTableSize 3097
DOSPageCount 2
DOSSiteCount 50
DOSPageInterval 1
DOSSiteInterval 1
DOSBlockingPeriod 10

Optionally you can also add the following directives:

DOSSystemCommand “su – someuser -c ‘/sbin/… %s …'”
DOSLogDir “/var/lock/mod_evasive”

You will also need to add this line if you are building with dynamic support:


AddModule mod_evasive.c


LoadModule evasive20_module modules/

(This line is already added to your configuration by apxs)


The hash table size defines the number of top-level nodes for each child’s
hash table. Increasing this number will provide faster performance by
decreasing the number of iterations required to get to the record, but
consume more memory for table space. You should increase this if you have
a busy web server. The value you specify will automatically be tiered up to
the next prime number in the primes list (see mod_evasive.c for a list
of primes used).


This is the threshhold for the number of requests for the same page (or URI)
per page interval. Once the threshhold for that interval has been exceeded,
the IP address of the client will be added to the blocking list.


This is the threshhold for the total number of requests for any object by
the same client on the same listener per site interval. Once the threshhold
for that interval has been exceeded, the IP address of the client will be added
to the blocking list.


The interval for the page count threshhold; defaults to 1 second intervals.


The interval for the site count threshhold; defaults to 1 second intervals.


The blocking period is the amount of time (in seconds) that a client will be
blocked for if they are added to the blocking list. During this time, all
subsequent requests from the client will result in a 403 (Forbidden) and
the timer being reset (e.g. another 10 seconds). Since the timer is reset
for every subsequent request, it is not necessary to have a long blocking
period; in the event of a DoS attack, this timer will keep getting reset.


If this value is set, an email will be sent to the address specified
whenever an IP address becomes blacklisted. A locking mechanism using /tmp
prevents continuous emails from being sent.

NOTE: Be sure MAILER is set correctly in mod_evasive.c
(or mod_evasive20.c). The default is “/bin/mail -t %s” where %s is
used to denote the destination email address set in the configuration.
If you are running on linux or some other operating system with a
different type of mailer, you’ll need to change this.


If this value is set, the system command specified will be executed
whenever an IP address becomes blacklisted. This is designed to enable
system calls to ip filter or other tools. A locking mechanism using /tmp
prevents continuous system calls. Use %s to denote the IP address of the
blacklisted IP.


Choose an alternative temp directory

By default “/tmp” will be used for locking mechanism, which opens some
security issues if your system is open to shell users.

In the event you have nonprivileged shell users, you’ll want to create a
directory writable only to the user Apache is running as (usually root),
then set this in your httpd.conf.

IP addresses of trusted clients can be whitelisted to insure they are never
denied. The purpose of whitelisting is to protect software, scripts, local
searchbots, or other automated tools from being denied for requesting large
amounts of data from the server. Whitelisting should *not* be used to add
customer lists or anything of the sort, as this will open the server to abuse.
This module is very difficult to trigger without performing some type of
malicious attack, and for that reason it is more appropriate to allow the
module to decide on its own whether or not an individual customer should be

To whitelist an address (or range) add an entry to the Apache configuration
in the following fashion:

DOSWhitelist 127.0.0.*

Wildcards can be used on up to the last 3 octets if necessary. Multiple
DOSWhitelist commands may be used in the configuration.


The keep-alive settings for your children should be reasonable enough to
keep each child up long enough to resist a DOS attack (or at least part of
one). Remember, it is the child processes that maintain their own internal
IP address tables, and so when one exits, so does all of the IP information it
had. For every child that exits, another 5-10 copies of the page may get
through before putting the attacker back into ‘403 Land’. With this said,
you should have a very high MaxRequestsPerChild, but not unlimited as this
will prevent cleanup.

You’ll want to have a MaxRequestsPerChild set to a non-zero value, as
DosEvasive cleans up its internal hashes only on exit. The default
MaxRequestsPerChild is usually 10000. This should suffice in only allowing
a few requests per 10000 per child through in the event of an attack (although
if you use DOSSystemCommand to firewall the IP address, a hole will no
longer be open in between child cycles).


Want to make sure it’s working? Run, and view the response codes.
It’s best to run it several times on the same machine as the web server until
you get 403 Forbidden messages. Some larger servers with high child counts
may require more of a beating than smaller servers before blacklisting

Please don’t use this script to DoS others without their permission.


– This module appears to conflict with the Microsoft Frontpage Extensions.
Frontpage sucks anyway, so if you’re using Frontpage I assume you’re asking
for problems, and not really interested in conserving server resources anyway.