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vyper performs double eval of raw_args in create_from_blueprint

Moderate severity GitHub Reviewed Published Apr 25, 2024 in vyperlang/vyper • Updated Jun 18, 2024

Package

pip vyper (pip)

Affected versions

< 0.4.0

Patched versions

0.4.0

Description

Summary

Using the create_from_blueprint builtin can result in a double eval vulnerability when raw_args=True and the args argument has side-effects.

A contract search was performed and no vulnerable contracts were found in production. In particular, the raw_args variant of create_from_blueprint was not found to be used in production.

Details

It can be seen that the _build_create_IR function of the create_from_blueprint builtin doesn't cache the mentioned args argument to the stack: https://github.com/vyperlang/vyper/blob/cedf7087e68e67c7bfbd47ae95dcb16b81ad2e02/vyper/builtins/functions.py#L1847

As such, it can be evaluated multiple times (instead of retrieving the value from the stack).

PoC

The vulnerability is demonstrated in the following boa test:

src1 = """
c: uint256
"""
deployer = """
created_address: public(address)
deployed: public(uint256)

@external
def get() -> Bytes[32]:
    self.deployed += 1
    return b''

@external
def create_(target: address):
    self.created_address = create_from_blueprint(target, raw_call(self, method_id("get()"), max_outsize=32), raw_args=True, code_offset=3)
"""

Factory = b.loads_partial(src1)
c = Factory.deploy_as_blueprint()

c2 = b.loads(deployer, b'')
c2.create_(c)
c2.deployed()

The output of c2.deployed() is 2 although create_ was called only once and the value was initialized to 0.

Patches

Patched in vyperlang/vyper#3976.

Impact

No vulnerable production contracts were found. Additionally, double evaluation of side-effects should be easily discoverable in client tests. As such, the impact is low.

References

@charles-cooper charles-cooper published to vyperlang/vyper Apr 25, 2024
Published by the National Vulnerability Database Apr 25, 2024
Published to the GitHub Advisory Database Apr 25, 2024
Reviewed Apr 25, 2024
Last updated Jun 18, 2024

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS score

0.043%
(10th percentile)

Weaknesses

CVE ID

CVE-2024-32647

GHSA ID

GHSA-3whq-64q2-qfj6

Source code

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