CVE-2019-1686 Explained : Impact and Mitigation

A vulnerability in the TCP flags inspection feature for access control lists (ACLs) on Cisco ASR 9000 Series Aggregation Services Routers could allow an unauthorized remote attacker to bypass protection provided by a configured ACL on an affected device.

Understanding CVE-2019-1686

This CVE involves a flaw in the TCP flags inspection feature for ACLs on Cisco ASR 9000 Series Routers, potentially enabling an attacker to circumvent ACL protection.

What is CVE-2019-1686?

The vulnerability arises from incorrect handling of ACLs on affected devices when Cisco Express Forwarding load balancing uses the 3-tuple hash algorithm, allowing unauthorized traffic to bypass configured ACLs.

The Impact of CVE-2019-1686

Attack Complexity: Low
Attack Vector: Network
Base Score: 5.8 (Medium Severity)
Integrity Impact: Low
Scope: Changed
No user interaction required

Technical Details of CVE-2019-1686

This section provides detailed technical information about the vulnerability.

Vulnerability Description

The flaw allows an attacker to send traffic through the affected device that would typically be denied by the configured ACL, bypassing the protection it offers.

Affected Systems and Versions

Product: Cisco IOS XR Software
Vendor: Cisco
Affected Versions: < 6.5.2, < 6.6.1

Exploitation Mechanism

Exploiting this vulnerability involves sending traffic through the affected device that would typically be denied by the configured ACL, enabling the attacker to bypass the protection offered.

Mitigation and Prevention

Steps to address and prevent exploitation of the vulnerability.

Immediate Steps to Take

Apply workarounds provided by Cisco to mitigate the vulnerability.
Implement ACL configurations to limit exposure.

Long-Term Security Practices

Regularly monitor and update ACL configurations.
Conduct security assessments to identify and address vulnerabilities.

Patching and Updates

Update affected systems to the fixed versions: 6.5.2 and later, 6.6.1 and later.