CVE-2017-15130 in Dovecot
Summary
by MITRE
A denial of service flaw was found in dovecot before 2.2.34. An attacker able to generate random SNI server names could exploit TLS SNI configuration lookups, leading to excessive memory usage and the process to restart.
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Analysis
by VulDB Data Team • 02/16/2023
The vulnerability identified as CVE-2017-15130 represents a critical denial of service weakness in the dovecot email server software prior to version 2.2.34. This flaw specifically targets the handling of Server Name Indication (SNI) during TLS connections, creating a scenario where malicious actors can trigger resource exhaustion and system instability. The vulnerability resides in the way dovecot processes SNI server names during the TLS handshake process, making it particularly dangerous for email servers that rely on SNI for proper certificate management and virtual hosting.
The technical implementation of this vulnerability stems from improper handling of SNI configuration lookups within the dovecot TLS subsystem. When an attacker generates random SNI server names, the dovecot service attempts to perform configuration lookups for each name, leading to exponential memory consumption as the system maintains lookup tables and processing structures for each unique SNI value. This memory exhaustion occurs because the dovecot service does not adequately limit or sanitize SNI inputs during the TLS negotiation phase, allowing attackers to consume system resources at an accelerated rate. The flaw is categorized under CWE-400 as an Uncontrolled Resource Consumption vulnerability, specifically manifesting as a memory exhaustion attack that can be executed through the manipulation of TLS SNI parameters.
The operational impact of CVE-2017-15130 extends beyond simple service disruption to potentially compromise the availability of email services for entire organizations. When exploited, this vulnerability can cause the dovecot process to consume all available memory resources, forcing automatic restarts and resulting in temporary unavailability of email services. This type of attack aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion. The vulnerability affects systems that utilize dovecot's TLS SNI capabilities for certificate management, particularly those running versions prior to 2.2.34, making it a widespread concern for email server administrators across various organizations.
Organizations affected by this vulnerability should prioritize immediate patching of their dovecot installations to version 2.2.34 or later, which contains the necessary fixes for proper SNI handling and memory management. System administrators should also implement network-level monitoring to detect unusual SNI patterns that might indicate exploitation attempts. The mitigation strategy should include configuring proper rate limiting for TLS connections and implementing firewall rules to restrict SNI-based attacks. Additionally, organizations should consider implementing intrusion detection systems that can identify and alert on suspicious SNI patterns, as this vulnerability can be exploited without authentication and can cause significant service disruption. The fix addresses the underlying memory management issue by implementing proper bounds checking and resource allocation controls during SNI processing, preventing the exponential memory consumption that previously occurred with random SNI inputs.