High-Severity Cisco DoS Flaw Can Immobilize ASR Routers

Cisco IOS XE Flaw

The flaw stems from an issue with the ingress packet processing function of Cisco IOS XR software.

A high-severity flaw in Cisco’s IOS XR software could allow unauthenticated, remote attackers to cripple Cisco Aggregation Services Routers (ASR).

The flaw stems from Cisco IOS XR, a train of Cisco Systems’ widely deployed Internetworking Operating System (IOS). The OS powers the Cisco ASR 9000 series, which are fully distributed routers engineered to address massive surges in video traffic.

“A successful exploit could cause the affected device to run out of buffer resources, which could make the device unable to process or forward traffic, resulting in a DoS [denial-of-service] condition,” according to a Tuesday security advisory by Cisco.

The flaw (CVE-2020-26070), which ranks 8.6 out of 10 on the CVSS scale, stems from an issue with the ingress packet processing function of Cisco IOS XR software. Ingress packet processing is a technique used to sort through incoming packets from different networks.

The vulnerability is due to improper resource allocation when an affected device processes network traffic. An attacker could exploit the flaw by sending specific streams of Layer 2 or Layer 3 protocol data units (PDUs) to an affected device, ultimately exhausting its buffer resources and crashing the device.

When a device is experiencing buffer resources exhaustion, the following message may be seen in the system logs: “%PKT_INFRA-spp-4-PKT_ALLOC_FAIL : Failed to allocate n packets for sending”

“This error message indicates that the device is not able to allocate buffer resources and forward network traffic in software switching mode,” said Cisco. “Customers are advised to contact their support organization to review the error messages and determine whether the device has been compromised by an exploitation of this vulnerability.”

The device would need to be restarted to regain functionality, said Cisco. This vulnerability affects Cisco ASR 9000 series routers if they are running a Cisco IOS XR Software release earlier than releases 6.7.2 or 7.1.2. Cisco fixed this vulnerability in Cisco IOS XR Software releases 6.7.2 and later and releases 7.1.2 and later.

Cisco patches

Updated Cisco IOS XR versions. Credit: Cisco

Of note, IOS Software, IOS XE Software, IOS XRv 9000 Router and NX-OS Software are not affected.

“The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory,” according to Cisco.

Cisco has recently dealt with various vulnerabilities across its product lines. Last week, Cisco disclosed a zero-day vulnerability in the Windows, macOS and Linux versions of its AnyConnect Secure Mobility Client Software. A few weeks ago, Cisco stomped out a severe flaw that can be exploited by an unauthenticated, remote attacker to launch a passel of malicious attacks — from denial of service (DoS) to cross-site request forgery (CSRF).

Cisco also recently sent out an advisory warning that a flaw (CVE-2020-3118) the Cisco Discovery Protocol implementation for Cisco IOS XR Software was being actively exploited by attackers. The bug, which could be exploited by unauthenticated, adjacent attackers, could allow them to execute arbitrary code or cause a reload on an affected device.

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