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denial of service

Security buffer overflow: libtk-img packages arbitrary code execution

It was discovered that a buffer overflow in the GIF image parsing code of Tk, a cross-platform graphical toolkit, could lead to denial of service and potentially the execution of arbitrary code. This is affected on all Linux / UNIX distributions.


Package : libtk-img
Vulnerability : buffer overflow
Problem type : local (remote)
Debian-specific: no
CVE Id(s) : CVE-2008-0553

Debian / Ubuntu Linux Fix

Type the following command:
# apt-get update
# apt-get upgrade

Ubuntu Linux Security Update: Samba regression ( CVE-2008-1105 )

A security issue affects the following Ubuntu releases:

=> Ubuntu 6.06 LTS
=> Ubuntu 7.04
=> Ubuntu 7.10
=> Ubuntu 8.04 LTS

This advisory also applies to the corresponding versions of Kubuntu, Edubuntu, and Xubuntu.

Samba developers discovered that nmbd could be made to overrun a buffer during the processing of GETDC logon server requests. When samba is configured as a Primary or Backup Domain Controller,
a remote attacker could send malicious logon requests and possibly cause a denial of service. (CVE-2007-4572)

Alin Rad Pop of Secunia Research discovered that Samba did not properly perform bounds checking when parsing SMB replies. A remote attacker could send crafted SMB packets and execute arbitrary code. (CVE-2008-1105)

How do I fix this issue?

Login as root and type the following two commands:
$ sudo apt-get update
$ sudo apt-get upgrade

FreeBSD Apache apr — multiple vulnerabilities

Some vulnerabilities have been reported in APR-util, which can be exploited by malicious users and malicious people to cause a DoS (Denial of Service).
[click to continue…]

Mambo Security Problems

Hackers (read as cracker) attacking on unpatched versions of the Mambo content management system that can be used to build botnets for use in phishing scams and distributed denial of service (DDoS) attacks.

They are using PHP-based CMS mass-exploitation and other vulnerabilities in open source CMS applications. If you are in server, collocation businesses then watch out all these attacks.

Update Mambo as soon as possible. More information available at following sites:

Linux Iptables Limit the number of incoming tcp connection / syn-flood attacks

A SYN flood is a form of denial-of-service attack in which an attacker sends a succession of SYN requests to a target's system. This is a well known type of attack and is generally not effective against modern networks. It works if a server allocates resources after receiving a SYN, but before it has received the ACK.

if Half-open connections bind resources on the server, it may be possible to take up all these resources by flooding the server with SYN messages. Syn flood is common attack and it can be block with following iptables rules:

iptables -A INPUT -p tcp --syn -m limit --limit 1/s --limit-burst 3 -j RETURN

All incoming connection are allowed till limit is reached:

  • --limit 1/s: Maximum average matching rate in seconds
  • --limit-burst 3: Maximum initial number of packets to match

Open our iptables script, add the rules as follows:

# Limit the number of incoming tcp connections
# Interface 0 incoming syn-flood protection
iptables -N syn_flood
iptables -A INPUT -p tcp --syn -j syn_flood
iptables -A syn_flood -m limit --limit 1/s --limit-burst 3 -j RETURN
iptables -A syn_flood -j DROP
#Limiting the incoming icmp ping request:
iptables -A INPUT -p icmp -m limit --limit  1/s --limit-burst 1 -j ACCEPT
iptables -A INPUT -p icmp -m limit --limit 1/s --limit-burst 1 -j LOG --log-prefix PING-DROP:
iptables -A INPUT -p icmp -j DROP
iptables -A OUTPUT -p icmp -j ACCEPT

First rule will accept ping connections to 1 per second, with an initial burst of 1. If this level crossed it will log the packet with PING-DROP in /var/log/message file. Third rule will drop packet if it tries to cross this limit. Fourth and final rule will allow you to use the continue established ping request of existing connection.

  • ‐‐limit rate: Maximum average matching rate: specified as a number, with an optional ‘/second’, ‘/minute’, ‘/hour’, or ‘/day’ suffix; the default is 3/hour.
  • ‐‐limit‐burst number: Maximum initial number of packets to match: this number gets recharged by one every time the limit specified above is not reached, up to this number; the default is 5.

You need to adjust the –limit-rate and –limit-burst according to your network traffic and requirements.

Let us assume that you need to limit incoming connection to ssh server (port 22) no more than 10 connections in a 10 minute:

iptables -I INPUT -p tcp -s 0/0 -d $SERVER_IP --sport 513:65535 --dport 22 -m state --state NEW,ESTABLISHED -m recent --set -j ACCEPT
iptables -I INPUT -p tcp --dport 22 -m state --state NEW -m recent --update --seconds 600 --hitcount 11 -j DROP
iptables -A OUTPUT -p tcp -s $SERVER_IP -d 0/0 --sport 22 --dport 513:65535 -m state --state ESTABLISHED -j ACCEPT

See also:

More information on recent patch can be found here