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Jetty Session ID Prediction Vulnerability
------------------------------------------------------------------------
SUMMARY
Different versions of Jetty, the popular java web server, are vulnerable
to a session id prediction attack.
DETAILS
Vulnerable Systems:
* Jetty versions prior to 4.2.27, 5.1.12, 6.0.2 and 6.1.0pre3
Immune Systems:
* Jetty versions 4.2.27, 5.1.12, 6.0.2 and 6.1.0pre3.
Jetty uses java.util.Random to generate session ids. The internal state of
this generator can be easily discovered, leading to an attacker being able
to hijack existing and future sessions.
java.util.random implements a linear congruential generator, of the
following form:
synchronized protected int next(int bits) {
seed = (seed * 0x5DEECE66DL + 0xBL) & ((1L << 48) - 1);
return (int)(seed >>> (48 - bits));
}
Jetty generates a 64-bit session id by generating two 32-bit numbers in
this way, so we end up with an encoded 64-bit integer. By decoding the
integer and splitting it into its two component 32-bit integers, we can
easily brute-force the generator's internal state. Once the state is
discovered, the generator can be run both forwards and backwards, so an
attacker can determine previously generated session ids, as well as
session ids that have not yet been generated. This allows the attacker to
hijack any existing session, and perform any actions that the original
user of the session could perform. Obviously the severity of this issue
varies from application to application but we believe it warrants at least
a "high" risk rating.
NGS have developed proof of concept code for this issue that implements a
session predictor for this bug. It takes a session id as input and outputs
candidates for the next 5 and previous 5 session ids. It is necessary to
output 7 candidate session ids for each iteration because Jetty encodes
the session id in a number base from 30 to 36 depending on the millisecond
in which the session id was generated. The underlying 64-bit integer is
the same, just represented in bases 30-36.
Here is some example output:
H:\jetty_rand\Debug>jetty_rand.exe g4sse9e7fs5ee
Radix: 30
Found seed: 5346772124980067
Session -5:
27s4jsk03074k
1gbb661e0l6mp
11ctqbu24shqo
nqqa46cv6ovh
h4xlr7d8n98c
cg9x29g6vfna
9568uhp0c7yw
Session -4:
586o97hbtkkis
3h9o0c9eglm5q
2dpgen12bekgo
1mf3ar81r4e7d
15vq2mdv83nmo
t13aedmjm4ts
lamwq2jurlzs
Session -3:
c2kqln033ior
8d98tft18mgj
5u715san1m0b
47rifnwhompl
31pb1t2496ef
27mbqm91n0gc
1mksf8xjn6kr
Session -2:
h5n7ft13ak1nr
biif83e4tlq37
7tj3f6tclak5h
5fpk27ulvu2nu
3s5vpubx7ekc9
2om684eem9iy2
1xf0lar1nqpwx
Session -1:
66isdajhm658g
463l7trqe65oo
2rodl8h2bjkb4
1wdl0j3wqr6tj
1d3hc9k0gm9ja
y8hj85q65rxq
p49erbpgioo4
Session 0:
g4sse9e7fs5ee
as3iaiqcjo82g
7eeb56egthkrm
54w87w5wtpwfk
3kdimj6vemoce
2iybbcyacjqk9
1t9qijf82uk52
The issue affects a great many products that are based on Jetty, such as
Apache Geronimo:
<http://geronimo.apache.org/> http://geronimo.apache.org/
The latest version (2.0) of Geronimo is not vulnerable to this issue.
Version 1.1 and prior are vulnerable however, and this issue can be used
to hijack a session to the administrative console.
A further 98 projects based on Jetty are listed on the Jetty website at:
<http://www.mortbay.com/powered.html> http://www.mortbay.com/powered.html
Fix:
This issue was fixed in the source code on the 22nd of November 2006, less
than 6 hours after it was reported. The issue is fixed in released
versions 4.2.27, 5.1.12, 6.0.2 and 6.1.0pre3.
The changes can be viewed here:
<http://fisheye.codehaus.org/changelog/jetty/?cs=1274>
http://fisheye.codehaus.org/changelog/jetty/?cs=1274
ADDITIONAL INFORMATION
The information has been provided by <mailto:nisr@ngssoftware.com>
NGSSoftware Insight Security Research.
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