CVE-2019-9636 in Sun ZFS Storage Appliance Kit
Summary
by MITRE
Python 2.7.x through 2.7.16 and 3.x through 3.7.2 is affected by: Improper Handling of Unicode Encoding (with an incorrect netloc) during NFKC normalization. The impact is: Information disclosure (credentials, cookies, etc. that are cached against a given hostname). The components are: urllib.parse.urlsplit, urllib.parse.urlparse. The attack vector is: A specially crafted URL could be incorrectly parsed to locate cookies or authentication data and send that information to a different host than when parsed correctly. This is fixed in: v2.7.17, v2.7.17rc1, v2.7.18, v2.7.18rc1; v3.5.10, v3.5.10rc1, v3.5.7, v3.5.8, v3.5.8rc1, v3.5.8rc2, v3.5.9; v3.6.10, v3.6.10rc1, v3.6.11, v3.6.11rc1, v3.6.12, v3.6.9, v3.6.9rc1; v3.7.3, v3.7.3rc1, v3.7.4, v3.7.4rc1, v3.7.4rc2, v3.7.5, v3.7.5rc1, v3.7.6, v3.7.6rc1, v3.7.7, v3.7.7rc1, v3.7.8, v3.7.8rc1, v3.7.9.
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Analysis
by VulDB Data Team • 06/06/2024
The vulnerability described in CVE-2019-9636 represents a critical issue in Python's handling of Unicode normalization during URL parsing operations. This flaw affects Python versions 2.7.x through 2.7.16 and 3.x through 3.7.2, specifically within the urllib.parse.urlsplit and urllib.parse.urlparse functions. The vulnerability stems from improper handling of Unicode encoding during NFKC (Normalization Form KC) normalization processes, which creates a condition where URLs containing specific Unicode characters are incorrectly parsed. This misinterpretation occurs when the netloc component of a URL contains Unicode characters that undergo incorrect normalization, leading to a fundamental misrepresentation of the host portion of the URL structure.
The technical impact of this vulnerability manifests as information disclosure through credential and session data leakage. When a maliciously crafted URL is processed through the affected Python functions, the incorrect parsing causes cookies, authentication tokens, and other sensitive data to be cached against a hostname that differs from the actual host to which the data should be sent. This creates a scenario where authentication information intended for one host could be inadvertently transmitted to an entirely different host, potentially enabling attackers to intercept sensitive session data, credentials, or cookies. The vulnerability operates at the protocol level where URL parsing and normalization interact with network security mechanisms, creating a path for data leakage through improper host identification during HTTP request processing.
The operational impact extends beyond simple credential theft to encompass broader security implications for web applications and services that rely on Python's standard library for URL handling. Applications using urllib.parse functions for URL validation, redirection, or authentication management become vulnerable to attacks where attackers can craft URLs that appear to target one host but actually cause data to be sent to a different host. This vulnerability particularly affects web applications that implement cookie management, session handling, or authentication flows that depend on host-based data caching mechanisms. The attack vector leverages the Unicode normalization behavior differences between Python versions, making it possible for attackers to exploit this issue in environments where Python is used for web scraping, API integration, or network communication components.
Mitigation strategies for CVE-2019-9636 require immediate updates to affected Python installations to versions that have implemented proper Unicode normalization handling. Organizations should prioritize upgrading to Python versions 2.7.17, 2.7.18, 3.5.10, 3.6.10, 3.6.11, 3.6.12, 3.7.3, 3.7.4, 3.7.5, 3.7.6, 3.7.7, 3.7.8, or 3.7.9, which contain the necessary fixes for proper NFKC normalization handling. Additionally, security teams should implement URL validation mechanisms that sanitize input URLs before processing, particularly when dealing with user-supplied data that might contain Unicode characters. The vulnerability aligns with CWE-170, which addresses improper handling of Unicode encoding, and represents a significant concern from an ATT&CK perspective under T1566, specifically targeting credential access through network-based attacks that exploit protocol implementation flaws. Organizations should also consider implementing network monitoring to detect unusual patterns in authentication data transmission that might indicate exploitation attempts, as the vulnerability creates opportunities for stealthy credential theft attacks.