CVE-2013-7040

Denial of Service in Python Hash Collision Handling

• CVSS 4.3
• CWE-310: Cryptographic Issues
• Cryptographic
• Local

Python 2.7 before 3.4 only uses the last eight bits of the prefix to randomize hash values, which causes it to compute hash values without restricting the ability to trigger hash collisions predictably and makes it easier for context-dependent attackers to cause a denial of service (CPU consumption) via crafted input to an application that maintains a hash table. NOTE: this vulnerability exists because of an incomplete fix for CVE-2012-1150.

CVE

CVE-2013-7040

CWE

CWE-310: Cryptographic Issues

CVSS base score

4.3

Published

2014-05-19

OWASP

A08 Software and Data Integrity Failures

Orthogonal defect classification

Algorithm

Code defect classification

Incorrect Algorithm

Category

Cryptographic

Subcategory

Inadequate random number generation

Accessibility scope

Local

Impact

Unauthorized Access

Fixed by upgrading

Yes

Solution

Upgrade to Python 3.4 or later.

import sys
table = {}
while True:
    s = input("Enter a string: ")
    if s == "quit":
        break
    h = hash(s)
    print(f"The hash of {s} is {h}")
    if h in table:
        print(f"Collision detected with {table[h]}")
        sys.exit(1)
    else:
        table[h] = s

import sys
import hashlib
table = {}
while True:
    s = input("Enter a string: ")
    if s == "quit":
        break
    h = hashlib.sha256(s.encode()).hexdigest()
    print(f"The hash of {s} is {h}")
    if h in table:
        print(f"Collision detected with {table[h]}")
        sys.exit(1)
    else:
        table[h] = s

@misc{vaitp:cve20137040,
  title        = {{Denial of Service in Python Hash Collision Handling}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2014},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2013-7040},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2013-7040/}}
}