CVE-2019-1686: Cisco ASR 9000 Series Aggregation Services Routers ACL Bypass Vulnerability

Severity: high (CVSS 8.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2019-04-17 · updated 2026-06-17
Weakness: CWE-284

Description

A vulnerability in the TCP flags inspection feature for access control lists (ACLs) on Cisco ASR 9000 Series Aggregation Services Routers could allow an unauthenticated, remote attacker to bypass protection offered by a configured ACL on an affected device. The vulnerability is due to incorrect processing of the ACL applied to an interface of an affected device when Cisco Express Forwarding load balancing using the 3-tuple hash algorithm is enabled. An attacker could exploit this vulnerability by sending traffic through an affected device that should otherwise be denied by the configured ACL. An exploit could allow the attacker to bypass protection offered by a configured ACL on the affected device. There are workarounds that address this vulnerability. Affected Cisco IOS XR versions are: Cisco IOS XR Software Release 5.1.1 and later till first fixed. First Fixed Releases: 6.5.2 and later, 6.6.1 and later.

Affected products

Cisco IOS XR Software: from 5.1.1 before 6.5.2; from 6.5.3 before 6.6.1 — fixed in 6.5.2, 6.6.1

How to fix

Upgrade to a fixed version: Cisco IOS XR Software 6.5.2, 6.6.1. Check the vendor advisory for mitigations.

References

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