CVE-2017-6791 in Unified Communications Manager
Summary
by MITRE
A vulnerability in the Trust Verification Service (TVS) of Cisco Unified Communications Manager could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to improper handling of Transport Layer Security (TLS) traffic by the affected software. An attacker could exploit this vulnerability by generating incomplete traffic streams. A successful exploit could allow the attacker to deny access to the TVS for an affected device, resulting in a DoS condition, until an administrator restarts the service. Known Affected Releases 10.0(1.10000.24) 10.5(2.10000.5) 11.0(1.10000.10) 9.1(2.10000.28). Cisco Bug IDs: CSCux21905.
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Analysis
by VulDB Data Team • 01/11/2021
The vulnerability described in CVE-2017-6791 represents a critical denial of service weakness within Cisco Unified Communications Manager's Trust Verification Service component. This flaw specifically targets the handling of Transport Layer Security traffic, creating an exploitable condition that allows remote attackers to disrupt critical communication services without requiring authentication credentials. The vulnerability stems from inadequate processing of TLS traffic streams, which creates a pathway for malicious actors to manipulate the system's operational state through carefully crafted incomplete traffic patterns. The affected versions including releases 10.0(1.10000.24), 10.5(2.10000.5), 11.0(1.10000.10), and 9.1(2.10000.28) demonstrate the widespread nature of this issue across multiple Cisco Unified Communications Manager iterations.
The technical exploitation mechanism involves generating incomplete TLS traffic streams that trigger improper state handling within the Trust Verification Service. This flaw falls under the category of improper input validation and resource management issues, aligning with CWE-20 - Improper Input Validation and CWE-400 - Uncontrolled Resource Consumption. When an attacker successfully crafts these malformed traffic patterns, the system fails to properly terminate or handle the incomplete TLS connections, leading to resource exhaustion or service instability. The vulnerability does not require authentication credentials due to the nature of the TLS processing flaw, making it particularly dangerous as it can be exploited from any remote location without prior access to the system. The attack vector operates through the network layer, targeting the specific TLS processing functionality that handles trust verification operations within the unified communications framework.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromising the reliability of enterprise communication systems. When exploited successfully, the vulnerability forces the Trust Verification Service to enter a degraded state where legitimate users cannot access the trust verification functionality, effectively creating a denial of service condition. This disruption can have cascading effects on unified communications services, as trust verification is fundamental to maintaining secure communication channels within the Cisco Unified Communications Manager environment. The requirement for administrator intervention to restart the service creates additional operational burden and potential downtime, particularly in mission-critical environments where communication availability is paramount. The vulnerability's exploitation typically results in service unavailability until manual intervention occurs, making it a significant concern for organizations relying on continuous communication infrastructure.
Mitigation strategies for this vulnerability should focus on immediate patching and configuration hardening measures. Cisco released specific software updates addressing this issue through the bug ID CSCux21905, which organizations should implement promptly across all affected systems. Network segmentation and access control measures can provide additional protection by limiting exposure to the vulnerable service. Implementing proper TLS configuration practices and monitoring for anomalous traffic patterns can help detect potential exploitation attempts. Security teams should also consider implementing intrusion detection systems capable of identifying malformed TLS traffic patterns associated with this specific vulnerability. The remediation process requires careful planning to minimize disruption while ensuring complete vulnerability resolution, particularly given the critical nature of the Trust Verification Service within unified communications environments. Organizations should also conduct thorough testing of patches in non-production environments before deployment to prevent unexpected service interruptions during the remediation process.