CVE-2025-26622

Vyper `sqrt()` may return rounded-up results due to oscillation. Upgrade to 0.4.1.

• CVSS 2.3
• CWE-682 Incorrect Calculation
• Numeric Errors
• Remote

vyper is a Pythonic Smart Contract Language for the EVM. Vyper `sqrt()` builtin uses the babylonian method to calculate square roots of decimals. Unfortunately, improper handling of the oscillating final states may lead to sqrt incorrectly returning rounded up results. This issue is being addressed and a fix is expected in version 0.4.1. Users are advised to upgrade as soon as the patched release is available. There are no known workarounds for this vulnerability.

CVE

CVE-2025-26622

CWE

CWE-682 Incorrect Calculation

CVSS base score

2.3

Published

2025-02-21

OWASP

A03:2021 Cryptographic Failures

Orthogonal defect classification

Algorithm

Code defect classification

Incorrect Algorithm

Category

Numeric Errors

Subcategory

Numeric Errors

Accessibility scope

Remote

Impact

Information Disclosure

Affected component

Vyper

Fixed by upgrading

Yes

Solution

Upgrade to Vyper version 0.4.1.

def sqrt(x):
    """Vulnerable function that demonstrates the security issue."""
    
    if x < 0:
        raise ValueError("Cannot calculate square root of a negative number")
    if x == 0:
        return 0

    guess = x
    next_guess = (guess + 1) // 2 

    for _ in range(100): 
        guess = next_guess
        next_guess = (guess + x // guess) // 2 

    return guess

def sqrt(x: int) -> int:
    """Secure function that fixes the vulnerability."""
    
    if x < 0:
        raise ValueError("Cannot calculate square root of negative number")
    if x == 0:
        return 0

    y = x
    z = (x + 1) // 2
    while z < y:
        y = z
        z = (x // z + z) // 2

    if (y + 1)**2 <= x:
       return y + 1
    else:
       return y

# This is a conceptual payload and might require adaptation based on the specific Vyper contract.
# It aims to exploit the oscillating final states issue in the sqrt() function.
# It relies on knowing an input value that triggers the rounding error.

# Example: Input value that is *suspected* to trigger the vulnerability.
# This value needs to be determined through analysis and testing of the vulnerable sqrt() implementation.
# The optimal input might depend on Vyper compiler version, EVM version, and other factors.
input_value = 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000  # Replace with a value found to be problematic.

# Vyper code snippet (Hypothetical contract vulnerable

@misc{vaitp:cve202526622,
  title        = {{Vyper `sqrt()` may return rounded-up results due to oscillation. Upgrade to 0.4.1.
}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2025},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2025-26622},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2025-26622/}}
}