AMNESIA:33: Researchers Disclose 33 Vulnerabilities Across Four Open Source TCP/IP Libraries

The vulnerabilities disclosed affect millions of Operational Technology, IoT and IT devices and include multiple remote code execution flaws.

Background

On December 8, researchers at Forescout published a report for 33 vulnerabilities that reportedly impact millions of devices. Dubbed AMNESIA:33, the vulnerabilities exist within four open TCP/IP libraries that are embedded in a number of Operational Technology (OT) and Internet of Things (IoT) devices as well as routers and printers. The four TCP/IP libraries affected by AMNESIA:33 include:

• uIP (integrated into Continki)
• FNET
• picoTCP
• Ethernut (Nut/Net)

Forescout estimates over 150 vendors that have implemented these libraries are affected by AMNESIA:33.

Additionally, the Cybersecurity and Infrastructure Security Agency (CISA) issued its own advisory for AMNESIA:33.

The 33 vulnerabilities include mostly Denial of Service and Information Leak vulnerabilities along with multiple remote code execution (RCE) flaws.

Analysis

The following is a breakdown of the 33 vulnerabilities, including the affected library, vulnerability type, common weakness enumeration, impact and CVSSv3 scores.

Remote Code Execution

Three out of the four TCP/IP libraries are affected by a RCE vulnerability, which means attackers could potentially execute code and gain full control over the devices.

CVE-2020-24336 is an out-of-bounds read vulnerability in the way the uIP library parses DNS records, as it does not perform any validation of the length field in the response, which could result in memory corruption.

CVE-2020-24338 is an out-of-bounds write vulnerability in the way the picoTCP library parses the domain name within DNS packets. Unlike CVE-2020-24336, which occurs when the uIP library attempts to read past the allocated memory buffer, CVE-2020-24338 occurs when the picoTCP library attempts to write past the allocated memory buffer, which could also result in memory corruption.

CVE-2020-25111 is an out-of-bounds write vulnerability in the Ethernut (Nut/Net) library due to multiple issues in the way the DNS handles queries and responses and lacks proper checks on null termination, data lengths and the number of queries and responses. Because of the lack of checks, these queries and responses may attempt to write past the allocated memory buffer, resulting in memory corruption.

DNS Cache Poisoning

In addition to the three RCE vulnerabilities outlined above, two of the libraries, uIP and FNET, are affected by DNS Cache Poisoning attacks. These are attacks that target the DNS cache, which stores requests made to certain resources locally to reduce latency. If an attacker is able to poison the cache, the next time a request is made to a legitimate resource (e.g. google.com), it would redirect the requester to a malicious resource (e.g. badwebsite.com) instead.

Denial of Service and Information Leak

The remaining flaws are primarily Denial of Service or Information Leak vulnerabilities.

Following in the footsteps of Ripple20 and URGENT/11

AMNESIA:33 follows in the footsteps of Ripple20 (disclosed in 2020) and URGENT/11 (disclosed in 2019).

Ripple20 is a set of 19 vulnerabilities in the TCP/IP library created by Treck, while URGENT/11 is a set of 11 vulnerabilities in VxWorks, a Real-Time Operating System (RTOS). Like AMNESIA:33, Ripple20 and URGENT/11 each reportedly affected millions of OT, IoT and IT devices.

Proof of concept

A section of the AMNESIA:33 report includes a proof-of-concept (PoC) for exploiting one of the three RCE vulnerabilities, CVE-2020-25111. At this time, no other PoCs have been shared publicly for the remaining vulnerabilities.

Solution

The researchers coordinated with the ICS-CERT and CERT/CC along with the Github Security team to attempt to address these vulnerabilities. According to the report, the following subset of the libraries received patches:

Additionally, open-iscsi, which implements some uIP code in its stack, has issued its own patches for it.

However, the original versions of uIP, Contiki and picoTCP did not receive patches as they have reached end-of-life.

CISA shares advisories from 13 vendors

In its own advisory, CISA shared advisories from the following 13 vendors that have implemented these TCP/IP libraries into their products:

• Devolo
• EMU Electronic AG
• FEIG
• Genetec
• Harting
• Hensoldt
• Microchip
• Nanotec
• NT-Ware
• Tagmaster
• Siemens
• Uniflow
• Yanzi Networks

Lessons learned from Ripple20 and URGENT/11

One of the overarching lessons learned from the disclosures of Ripple20 and URGENT11 is that the broad usage of open source TCP/IP libraries across a number of devices means that these vulnerabilities will persist for quite some time. The researchers collaborate with entities like ICS-CERT and the CERT Coordination Center (CERT/CC) to aid in the identification and notification process, but this is an extensive process. Knowing which devices are impacted will be a continuous effort, but if you’re a vendor that has implemented one of these libraries, it is imperative that you seek out the developers of those libraries and implement these patched versions immediately to protect your customers.

Identifying affected systems

Tenable is working to implement product coverage for the AMNESIA:33 vulnerabilities across our suite of products, including Tenable.ot. A list of Tenable plugins to identify these vulnerabilities will appear here as they’re released.

Get more information

• AMNESIA:33 Report
• ICS-CERT (CISA) Alert for AMNESIA:33

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