CVE-2021-27633 in NetWeaver AS for ABAP
Summary
by MITRE • 06/09/2021
SAP NetWeaver AS for ABAP (RFC Gateway), versions - KRNL32NUC - 7.22,7.22EXT, KRNL64NUC - 7.22,7.22EXT,7.49, KRNL64UC - 8.04,7.22,7.22EXT,7.49,7.53,7.73, KERNEL - 7.22,8.04,7.49,7.53,7.73,7.77,7.81,7.82,7.83, allows an unauthenticated attacker without specific knowledge of the system to send a specially crafted packet over a network which will trigger an internal error in the system due to improper input validation in method ThCPIC() causing the system to crash and rendering it unavailable. In this attack, no data in the system can be viewed or modified.
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Analysis
by VulDB Data Team • 06/11/2021
SAP NetWeaver AS for ABAP systems running various kernel versions are vulnerable to a critical denial of service condition represented by CVE-2021-27633. This vulnerability specifically affects the RFC Gateway component within the system architecture and manifests through improper input validation within the ThCPIC() method. The flaw exists in multiple kernel versions including KRNL32NUC 7.22 and 7.22EXT, KRNL64NUC 7.22, 7.22EXT, and 7.49, KRNL64UC 8.04, 7.22, 7.22EXT, 7.49, 7.53, and 7.73, as well as various KERNEL versions 7.22, 8.04, 7.49, 7.53, 7.73, 7.77, 7.81, 7.82, and 7.83. The vulnerability operates at the network level and can be exploited by unauthenticated attackers who do not require specific system knowledge or credentials to execute the attack.
The technical mechanism behind this vulnerability involves a specially crafted network packet that triggers an internal error within the system's processing logic. When the ThCPIC() method receives malformed input, it fails to properly validate the incoming data and subsequently crashes the system. This improper input validation represents a classic weakness that falls under CWE-20, which describes "Improper Input Validation" as a fundamental security flaw that allows attackers to manipulate system behavior through malformed data inputs. The vulnerability specifically impacts the RFC (Remote Function Call) Gateway functionality, which serves as a critical communication interface between SAP systems and external applications, making it a prime target for disruption attacks.
The operational impact of this vulnerability is significant as it enables a remote attacker to render the affected SAP system completely unavailable through a simple network-based attack. The system crash occurs without any data disclosure or modification capabilities, meaning that while the availability is compromised, the integrity and confidentiality of the system data remain protected. However, the denial of service aspect creates substantial business disruption, as SAP NetWeaver systems typically serve as critical infrastructure components for enterprise operations. This vulnerability can be particularly damaging in mission-critical environments where system uptime is essential for business continuity. The attack requires no authentication, no specific system knowledge, and can be executed by anyone with network access to the target system, making it extremely dangerous in production environments.
Organizations affected by CVE-2021-27633 should implement immediate mitigations while awaiting official patches from SAP. The primary recommendation involves applying the relevant security patches released by SAP for the affected kernel versions. System administrators should also consider implementing network-level controls such as firewall rules to restrict access to RFC gateway ports and ports used by the affected system components. Monitoring network traffic for unusual patterns and implementing intrusion detection systems can help identify potential exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which covers "Endpoint Termination: Network Denial of Service," and represents a common attack vector that leverages improper input validation to cause system instability. Organizations should also conduct thorough network segmentation to limit the attack surface and implement proper access controls to reduce the risk of exploitation. The vulnerability demonstrates the importance of input validation in critical system components and highlights the need for robust security testing of network-facing services to prevent similar issues in the future.