CVE-2017-3887 in Firepower System Software
Summary
by MITRE
A vulnerability in the detection engine that handles Secure Sockets Layer (SSL) packets for Cisco Firepower System Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition because the Snort process unexpectedly restarts. This vulnerability affects Cisco Firepower System Software prior to the first fixed release when it is configured with an SSL Decrypt-Resign policy. More Information: CSCvb62292. Known Affected Releases: 6.0.1 6.1.0 6.2.0. Known Fixed Releases: 6.2.0 6.1.0.2.
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Analysis
by VulDB Data Team • 04/08/2017
The vulnerability identified as CVE-2017-3887 resides within the detection engine of Cisco Firepower System Software, specifically impacting the handling of Secure Sockets Layer packets. This weakness manifests when the system operates with an SSL Decrypt-Resign policy configuration, creating a critical exposure point for remote attackers. The flaw operates at the core of the Snort intrusion detection system component that processes SSL traffic, making it particularly dangerous as it affects the fundamental security monitoring capabilities of the firewall appliance. The vulnerability stems from improper handling of malformed SSL packets that triggers unexpected behavior in the detection engine's processing logic.
The technical implementation of this vulnerability exploits the SSL packet processing mechanism within the Cisco Firepower system's detection engine. When an attacker sends specifically crafted SSL packets to a vulnerable system configured with SSL Decrypt-Resign policy, the Snort process experiences an unexpected restart that results in a complete denial of service condition. This occurs because the detection engine fails to properly validate or handle certain edge cases in SSL packet structures, leading to a crash of the Snort daemon. The vulnerability is particularly insidious because it requires no authentication credentials for exploitation, allowing any remote attacker to trigger the condition from outside the network perimeter. The flaw demonstrates characteristics consistent with a buffer overflow or improper input validation issue that falls under CWE-125, which represents out-of-bounds read conditions.
The operational impact of CVE-2017-3887 extends beyond simple service interruption as it compromises the core security monitoring functionality of the Cisco Firepower system. Organizations relying on this protection platform for network security would experience complete loss of SSL traffic inspection capabilities, leaving encrypted malicious traffic undetected and potentially allowing attackers to bypass other security controls. The unexpected restart of the Snort process creates a cascading effect where legitimate security monitoring ceases entirely, potentially masking other attacks or security incidents that would normally be detected by the system. This vulnerability particularly affects organizations using Cisco Firepower appliances in their perimeter security infrastructure, where the loss of SSL decryption capabilities could expose sensitive network communications to undetected threats. The DoS condition is persistent and requires manual intervention to restore normal operation, creating extended periods of reduced security posture.
Mitigation strategies for CVE-2017-3887 require immediate implementation of the vendor-provided software updates to the affected Cisco Firepower System Software versions. Organizations should prioritize upgrading to the fixed releases 6.1.0.2 and 6.2.0, as these versions contain patches specifically addressing the SSL packet handling flaw. Network administrators should also consider implementing temporary network segmentation to limit exposure while updates are deployed, though this approach only provides partial protection. The vulnerability's characteristics align with ATT&CK technique T1499.002, which involves network denial of service attacks, making it particularly relevant for organizations monitoring for such threats. Additionally, implementing network monitoring to detect abnormal Snort process restarts could help identify exploitation attempts before they cause complete service disruption. Security teams should also review their SSL Decrypt-Resign policy configurations to determine if the functionality is necessary for their security requirements, potentially reducing the attack surface by disabling the vulnerable feature entirely.