CVE-2021-33683 in Web Dispatcher
Summary
by MITRE • 07/14/2021
SAP Web Dispatcher and Internet Communication Manager (ICM), versions - KRNL32NUC 7.21, 7.21EXT, 7.22, 7.22EXT, KRNL32UC 7.21, 7.21EXT, 7.22, 7.22EXT, KRNL64NUC 7.21, 7.21EXT, 7.22, 7.22EXT, 7.49, KRNL64UC 7.21, 7.21EXT, 7.22, 7.22EXT, 7.49, 7.53, 7.73, WEBDISP 7.53, 7.73, 7.77, 7.81, 7.82, 7.83, KERNEL 7.21, 7.22, 7.49, 7.53, 7.73, 7.77, 7.81, 7.82, 7.83, process invalid HTTP header. The incorrect handling of the invalid Transfer-Encoding header in a particular manner leads to a possibility of HTTP Request Smuggling attack. An attacker could exploit this vulnerability to bypass web application firewall protection, divert sensitive data such as customer requests, session credentials, etc.
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Analysis
by VulDB Data Team • 07/18/2021
SAP Web Dispatcher and Internet Communication Manager components contain a critical vulnerability in their HTTP header processing mechanisms that enables HTTP Request Smuggling attacks. This flaw exists in multiple kernel versions including KRNL32NUC 7.21 through 7.22EXT, KRNL32UC 7.21 through 7.22EXT, KRNL64NUC 7.21 through 7.49, KRNL64UC 7.21 through 7.49 and 7.53, WEBDISP 7.53 through 7.83, and KERNEL 7.21 through 7.83. The vulnerability specifically manifests when these systems process invalid Transfer-Encoding headers in a particular manner that creates ambiguity in request parsing between the client and server components.
The technical flaw stems from improper validation and handling of malformed HTTP Transfer-Encoding headers, which creates a parsing inconsistency that attackers can exploit. When an attacker sends a malformed request containing conflicting Transfer-Encoding directives, the system's inconsistent interpretation of these headers creates a window where the attacker can inject additional requests or manipulate the flow of legitimate traffic. This behavior aligns with CWE-444 HTTP Request Smuggling vulnerability classification, which specifically addresses inconsistencies in HTTP message parsing that allow attackers to separate requests and responses.
The operational impact of this vulnerability is severe as it enables attackers to bypass web application firewall protections that rely on proper HTTP request parsing. Attackers can manipulate the system to forward requests to unintended destinations, potentially redirecting sensitive customer data, session credentials, and other confidential information. The vulnerability creates a persistent threat vector that can be exploited for data exfiltration, session hijacking, and unauthorized access to protected resources. This type of attack falls under the ATT&CK technique T1566.002 for Phishing with Spoofed Credentials and T1071.004 for Application Layer Protocol HTTP, as it leverages HTTP protocol inconsistencies to bypass security controls.
Organizations should immediately implement mitigations including strict HTTP header validation, enabling comprehensive logging of HTTP request processing, and deploying web application firewalls with enhanced HTTP parsing capabilities. Network segmentation and monitoring of suspicious HTTP traffic patterns can help detect exploitation attempts. SAP has released patches for affected versions, and organizations should prioritize upgrading to patched releases while implementing additional defensive measures such as request smuggling detection mechanisms and enhanced access controls for critical systems. The vulnerability represents a significant risk to data integrity and confidentiality, particularly in environments where these components serve as front-line security defenses.