CVE-2023-1108 in Communications Cloud Native Core Unified Data Repository
Summary
by MITRE • 09/14/2023
A flaw was found in undertow. This issue makes achieving a denial of service possible due to an unexpected handshake status updated in SslConduit, where the loop never terminates.
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Analysis
by VulDB Data Team • 06/26/2025
The vulnerability identified as CVE-2023-1108 resides within the Undertow web server implementation, specifically affecting the SSL/TLS handshake processing mechanism. This flaw manifests in the SslConduit component where an unexpected handshake status update creates a condition that prevents proper termination of a processing loop. The issue stems from inadequate state management during SSL connection establishment, particularly when handling certain handshake sequences that trigger the problematic code path. The vulnerability represents a classic denial of service scenario where the system becomes trapped in an infinite loop, consuming excessive CPU resources and preventing legitimate connection handling. This type of vulnerability falls under CWE-835, which specifically addresses loop termination issues that can lead to denial of service conditions. The flaw demonstrates poor error handling and state transition management within the SSL processing pipeline, creating a scenario where malformed or unexpected handshake sequences can cause the server to become unresponsive.
The technical execution of this vulnerability occurs when the SslConduit component receives an SSL handshake message that triggers an unexpected status update during the SSL/TLS negotiation process. This update causes the loop responsible for processing the handshake to enter a state where it cannot properly evaluate its termination condition, resulting in continuous iteration without progress. The issue is particularly concerning because SSL/TLS handshakes are fundamental to secure communication and occur frequently during normal server operation. When this loop fails to terminate, it effectively blocks the thread or process responsible for handling the connection, preventing it from processing subsequent requests or completing the current connection establishment. The vulnerability can be triggered through various means including malformed SSL handshake packets, unexpected handshake sequence transitions, or specific timing conditions that cause the SslConduit to update its internal state in an unexpected manner.
The operational impact of CVE-2023-1108 extends beyond simple resource exhaustion to potentially compromise the availability and reliability of affected systems. Servers running vulnerable versions of Undertow become susceptible to sustained denial of service attacks where attackers can send carefully crafted SSL handshake sequences to trigger the infinite loop condition. This vulnerability affects web applications and services that rely on Undertow as their underlying HTTP server implementation, potentially impacting a wide range of enterprise applications, web services, and API endpoints. The continuous CPU consumption caused by the non-terminating loop can lead to system instability, performance degradation, and complete service unavailability. From an attacker perspective, this represents a low-effort, high-impact method of causing service disruption since the vulnerability can be exploited through standard SSL/TLS connection attempts without requiring privileged access or complex exploitation techniques. The vulnerability also aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how improper state management in cryptographic libraries can create systemic security weaknesses.
Mitigation strategies for CVE-2023-1108 should focus on both immediate patching and operational hardening measures. The primary solution involves updating to a patched version of Undertow where the SSL handshake processing logic has been corrected to properly handle all expected status transitions and ensure loop termination under all conditions. Organizations should prioritize patching their Undertow implementations to prevent exploitation, particularly in production environments where the vulnerability could be leveraged for sustained denial of service attacks. In addition to patching, network-level mitigations such as rate limiting SSL handshake attempts, implementing connection timeouts, and deploying intrusion detection systems can help detect and limit the impact of exploitation attempts. Monitoring for unusual CPU utilization patterns and connection handling behavior can serve as early warning indicators of potential exploitation. The vulnerability also highlights the importance of proper input validation and state management in cryptographic implementations, emphasizing the need for thorough testing of edge cases in security-critical code paths. Organizations should conduct vulnerability assessments to identify all systems using vulnerable Undertow versions and implement comprehensive monitoring to detect potential exploitation attempts. This vulnerability demonstrates how seemingly minor state management issues in security libraries can create significant availability risks, reinforcing the importance of robust error handling and termination conditions in all security-related code components.