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Thrangrycat: Vulnerabilities in Cisco Secure Boot and Cisco IOS XE (CVE-2019-1649, CVE-2019-1862)

Researchers identify vulnerabilities in Cisco Secure Boot process and Cisco IOS XE devices that could reportedly be chained together for significant impact.

Background

On May 13, Cisco published two security advisories for vulnerabilities in Cisco Secure Boot and Cisco IOS XE. Researchers at security firm Red Balloon Security, Inc. discovered and reported the vulnerabilities to Cisco’s Product Security Incident Response Team (PSIRT) in November 2018. The security firm refers to the Secure Boot vulnerability by three angry cat emojis (😾 😾 😾) instead of a name, but says that a “suitable enunciation” of the emojis is Thrangrycat.

Analysis

😾 😾 😾 or Thrangrycat (CVE-2019-1649) is an authenticated hardware tampering vulnerability in the Field Programmable Gate Array (FPGA) for Cisco’s Secure Boot process. If a local attacker were to exploit this vulnerability, they would be able to render a vulnerable device unusable or implant a malicious firmware image on it.

CVE-2019-1862 is an authenticated command injection vulnerability in Cisco IOS XE’s web-based user interface caused by improper sanitization of user-supplied input. A remote attacker who exploits this vulnerability would be able to execute commands as root on affected devices.

Red Balloon Security Inc. says Thrangrycat bypasses Cisco’s Trust Anchor module (TAm) that underpins Cisco’s Secure Boot process, but Cisco has publicly disputed the claim that it affects Trust Anchor.

According to Red Balloon’s disclosure, chaining the two vulnerabilities together reportedly enables a remote attacker to bypass Cisco’s Secure Boot and “lock out all future software updates to the TAm.”

Proof of concept

Cisco’s PSIRT team is aware of proof-of-concept (PoC) code for Cisco ASR 1001-X devices as well as for IOS XE software. These were likely shared with them by the Red Balloon Security team. However, they are currently unaware of any PoCs in the wild.

Solution

Cisco released a patch for CVE-2019-1862 for Cisco IOS XE and also provided a tool called Cisco IOS Software Checker to identify vulnerabilities in Cisco IOS and IOS XE.

For Thrangrycat, Cisco says it is working on patches, but notes that the patch won’t be a straightforward update for most devices as it will require “on-premise[s] reprogramming of a low-level hardware component.”

The security advisory for Thrangrycat lists 53 Bug IDs under the Affected Products section, which includes Cisco ASA 5500-X Series with FirePOWER Services, Cisco Firepower 2100, 4000 and 9000 series, as well as other Cisco routers, switches and network interface modules. Patches for these devices will be released anywhere between May 2019 and November 2019. Please refer to the advisory page for more details on planned firmware availability.

Identifying affected systems

A list of Nessus plugins to identify these vulnerabilities will appear here as they’re released.

Please note that the link above will contain newer plugins over time as Cisco releases newer patches throughout the year.

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