CVE-2020-14422 in Python
Summary
by MITRE
Lib/ipaddress.py in Python through 3.8.3 improperly computes hash values in the IPv4Interface and IPv6Interface classes, which might allow a remote attacker to cause a denial of service if an application is affected by the performance of a dictionary containing IPv4Interface or IPv6Interface objects, and this attacker can cause many dictionary entries to be created.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 10/25/2020
The vulnerability identified as CVE-2020-14422 resides within Python's standard library implementation of the ipaddress module, specifically affecting versions through 3.8.3. This flaw manifests in the hash computation methods of IPv4Interface and IPv6Interface classes, creating a potential denial of service condition that can severely impact applications relying on dictionary operations with these network address objects. The issue stems from the improper handling of hash values that can lead to hash collision attacks, where multiple objects produce identical hash codes, causing dictionary performance degradation.
The technical implementation flaw occurs when applications utilize dictionaries or sets containing IPv4Interface or IPv6Interface objects, particularly when these collections grow large enough to trigger hash table collision scenarios. The hash computation algorithm fails to properly distribute hash values across the hash table space, creating predictable collision patterns that allow an attacker to craft specific input sequences. This vulnerability operates under the weakness category of CWE-327, which deals with use of a broken or risked cryptographic algorithm, and more specifically relates to weak hash functions that can be exploited for denial of service attacks. The vulnerability directly maps to ATT&CK technique T1499.004, which involves network denial of service through resource exhaustion.
When exploited, this vulnerability can cause significant operational impact on applications that depend on dictionary lookups with network address objects. An attacker who can influence the creation of dictionary entries containing IPv4Interface or IPv6Interface objects can force hash collisions, leading to quadratic time complexity in dictionary operations instead of the expected linear performance. This degradation can result in application slowdowns, unresponsiveness, or complete denial of service, particularly in scenarios where applications process large volumes of network data or where attackers can inject malicious network addresses. The impact is most severe in applications that maintain lookup tables of network addresses, such as network monitoring systems, firewalls, or any service that processes network traffic data structures.
The recommended mitigation strategy involves upgrading to Python version 3.8.4 or later, where the hash computation has been corrected to properly distribute hash values across the available hash space. Organizations should also implement input validation measures to limit the number of dictionary entries that can be created by untrusted sources, and consider rate limiting or other protective measures when processing network address data. Additionally, developers should avoid creating large dictionaries containing IPv4Interface or IPv6Interface objects without proper safeguards, and implement alternative data structures when high performance is critical. Security teams should monitor their Python applications for usage patterns that might expose them to this vulnerability, particularly in environments where network address processing is a core function. The fix implemented in Python 3.8.4 addresses the underlying hash computation algorithm to ensure proper distribution of hash values, eliminating the predictable collision patterns that enabled the denial of service attack vector.