CVE-2017-7671 in Traffic Server
Summary
by MITRE
There is a DOS attack vulnerability in Apache Traffic Server (ATS) 5.2.0 to 5.3.2, 6.0.0 to 6.2.0, and 7.0.0 with the TLS handshake. This issue can cause the server to coredump.
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Analysis
by VulDB Data Team • 01/09/2020
Apache Traffic Server suffers from a denial of service vulnerability during the TLS handshake process that affects multiple version ranges including 5.2.0 through 5.3.2, 6.0.0 through 6.2.0, and 7.0.0. This vulnerability represents a critical flaw in the server's secure communication handling mechanism that can be exploited by remote attackers to disrupt service availability. The issue manifests when the server encounters malformed or specially crafted TLS handshake messages that trigger an unexpected termination condition leading to a core dump. The vulnerability stems from insufficient input validation and error handling within the TLS protocol implementation, particularly during the initial negotiation phase where client and server establish secure communication parameters. When an attacker sends malformed TLS handshake records or exploits specific edge cases in the protocol parsing logic, the server process crashes and terminates abruptly, resulting in complete service disruption. This weakness falls under the CWE-248 category of "Uncaught Exception" and aligns with ATT&CK technique T1499.004 for network denial of service attacks. The impact extends beyond simple service interruption as the core dump generation can consume significant system resources and potentially reveal sensitive information about the server configuration. Network administrators should note that this vulnerability can be exploited without authentication, making it particularly dangerous in environments where ATS serves as a critical edge component. The flaw demonstrates poor defensive programming practices where error conditions during cryptographic protocol negotiation are not properly managed, leading to process termination rather than graceful error handling or connection rejection.
The technical exploitation of this vulnerability requires minimal prerequisites as attackers only need to establish a TLS connection to the affected server and send carefully crafted handshake messages that trigger the memory corruption or invalid state condition. The server's TLS implementation fails to properly validate the sequence and structure of handshake messages, allowing malicious inputs to bypass normal protocol validation checks. During the TLS handshake, ATS processes various message types including client hello, server hello, certificate, and key exchange messages, but the parsing logic for certain message combinations or malformed parameters causes the server to enter an undefined state where it cannot continue processing legitimate connections. The core dump generation indicates that the server's memory management system detects an unrecoverable error condition and triggers an immediate process termination to prevent further corruption. This behavior represents a fundamental flaw in the server's fault tolerance and resilience design, as a single malicious connection attempt can bring down the entire service. The vulnerability's presence in multiple major version lines suggests that the underlying code pattern causing the issue was not properly addressed during the development lifecycle, indicating potential architectural problems in the TLS stack implementation. Organizations should recognize that this vulnerability can be automated and scaled across multiple connections, potentially enabling distributed denial of service attacks that could overwhelm system resources during recovery phases.
Mitigation strategies for this vulnerability should focus on immediate patching of affected versions to address the root cause in the TLS implementation. System administrators should prioritize upgrading to versions that contain the specific fixes for the TLS handshake error handling, as these patches typically include enhanced input validation and proper exception handling mechanisms. The recommended approach includes implementing network-level protections such as rate limiting and connection throttling to reduce the impact of potential exploitation attempts. Organizations should also consider deploying intrusion detection systems that can monitor for unusual TLS handshake patterns or malformed connection attempts that may indicate exploitation attempts. Configuration changes such as disabling vulnerable TLS versions or implementing stricter certificate validation policies can provide additional layers of defense. The fix for this vulnerability typically involves strengthening the TLS protocol parser to gracefully handle malformed inputs without terminating the process, which aligns with security best practices outlined in the OWASP Top Ten and NIST SP 800-53 security controls. Additionally, implementing comprehensive logging and monitoring for TLS handshake failures can help detect exploitation attempts and provide forensic evidence for incident response activities. Regular security assessments of the ATS configuration should include validation of TLS implementation robustness and testing of various error conditions to ensure proper handling without system termination. The vulnerability serves as a reminder of the critical importance of secure coding practices in cryptographic implementations and the necessity of thorough testing for error conditions in security-sensitive components.