CVE-2016-1494
Spoofing vulnerability in Python-RSA's verify function
- CVSS 5.3
- CWE-20: Improper Input Validation
- Cryptographic
- Remote
The verify function in the RSA package for Python (Python-RSA) before 3.3 allows attackers to spoof signatures with a small public exponent via crafted signature padding, aka a BERserk attack.
- CVSS base score
- 5.3
- Published
- 2016-01-13
- OWASP
- A08 Software and Data Integrity Failures
- Orthogonal defect classification
- Algorithm
- Code defect classification
- Incorrect Algorithm
- Category
- Cryptographic
- Subcategory
- Cryptographic Implementation Error
- Accessibility scope
- Remote
- Impact
- Denial of Service (DoS)
- Fixed by upgrading
- Yes
Solution
Upgrade to Python-RSA version 3.3 or later.
Vulnerable code sample
import rsa
import binascii
pubkey = rsa.PublicKey(0x10001, 0x10001)
message = b"Hello, world!"
signature = binascii.unhexlify(b"0001ff003031300d06096086480165030402010500042014d9277c9e99f543e2a5d13e0d81f3b2110f9a4ac")
def verify(message, signature, pubkey):
message = rsa.transform.bytes2int(message)
encrypted = rsa.core.encrypt_int(signature, pubkey.e, pubkey.n)
clearsig = rsa.transform.int2bytes(encrypted, rsa.common.byte_size(pubkey.n))
return message == rsa.transform.bytes2int(clearsig[-len(message):])
print(verify(message, signature, pubkey))Patched code sample
import rsa
import binascii
pubkey = rsa.PublicKey(0x10001, 0x10001)
message = b"Hello, world!"
signature = binascii.unhexlify(b"0001ff003031300d06096086480165030402010500042014d9277c9e99f543e2a5d13e0d81f3b2110f9a4ac")
def verify(message, signature, pubkey):
if pubkey.e == 3:
raise ValueError("Insecure public exponent (e=3) detected. Possible signature forgery attempt.")
if len(signature) < 128:
raise ValueError("Signature too short, potential forgery attempt.")
message = rsa.transform.bytes2int(message)
encrypted = rsa.core.encrypt_int(signature, pubkey.e, pubkey.n)
clearsig = rsa.transform.int2bytes(encrypted, rsa.common.byte_size(pubkey.n))
if not clearsig.startswith(b'\x00\x01\xff\x00'):
raise ValueError("Invalid PKCS#1 v1.5 padding, possible forgery detected.")
return message == rsa.transform.bytes2int(clearsig[-len(message):])
try:
print(verify(message, signature, pubkey))
except ValueError as e:
print(f"Verification failed: {e}")Cite this entry
@misc{vaitp:cve20161494,
title = {{Spoofing vulnerability in Python-RSA's verify function}},
author = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
year = {2016},
note = {VAITP Python Vulnerability Dataset, entry CVE-2016-1494},
howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2016-1494/}}
}Introducing the "VAITP dataset": a specialized repository of Python vulnerabilities and patches, meticulously compiled for the use of the security research community. As Python's prominence grows, understanding and addressing potential security vulnerabilities become crucial. Crafted by and for the cybersecurity community, this dataset offers a valuable resource for researchers, analysts, and developers to analyze and mitigate the security risks associated with Python. Through the comprehensive exploration of vulnerabilities and corresponding patches, the VAITP dataset fosters a safer and more resilient Python ecosystem, encouraging collaborative advancements in programming security.
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