CVE-2022-22195 is a serious vulnerability found in the kernel of Juniper Networks Junos OS Evolved. It allows unauthenticated, remote attackers to exploit an improper update of reference counts—leading to a counter overflow and eventually a Denial of Service (DoS) on affected devices. In this post, we’ll break down the vulnerability, show a simplified example of similar code logic, discuss the potential impact, show how attackers can exploit it, and list official resources for further reading.

What Is CVE-2022-22195?

At its core, this is a classic reference count overflow bug. When certain internal kernel data structures are referenced and then released, their usage is tracked by an integer variable—a reference counter. If this counter isn’t handled carefully and overflows (for example, goes past its maximum value and wraps around to zero), the system may mistakenly free memory regions that are still in use, causing system instability or a crash.

21.3 versions before 21.3R2-EVO

Good news:

Junos OS (the classic version, not Evolved): Not affected

References:  
- Juniper Security Advisory  
- NVD entry

Why Does This Happen?

When many clients or requests hit a Junos OS Evolved router at the same time, each might increment the reference counter for certain kernel objects (e.g., sessions, routes, etc). If the attacker can cause the counter to overflow—usually by sending a ton of requests in a short time—they can either trick the system into deallocating memory in use or exhaust resources until the system becomes unresponsive, leading to a Denial of Service.

Imagine a simple C-like pattern

struct my_obj {
    int ref_count;
    // ... other fields ...
};

void acquire_obj(struct my_obj *obj) {
    obj->ref_count++; // Increment reference count, but no upper bound check
}

void release_obj(struct my_obj *obj) {
    obj->ref_count--; // Decrement
    if (obj->ref_count == ) {
        free(obj); // Free when reference count reaches zero
    }
}

If an attacker causes ref_count to overflow

2147483647 (max int) + 1 = -2147483648 (wraps to a negative value!)

Systems relying on the reference count could free or reuse memory incorrectly, leading to crashes and instability.

Step-by-Step: Typical Attack Scenario

1. Find a weak spot: The attacker identifies a network protocol or API endpoint that, when called, causes the reference count to increase. This could be anything—from new session requests to specific packet types.

2. Blast with requests: They flood the device with thousands or millions of requests—each incrementing the counter.

3. Force an overflow: When the counter limit is exceeded (e.g., a 32-bit signed integer goes from 2147483647 to -2147483648), the logic for object management breaks.

4. Trigger a crash: The device kernel could accidentally free memory that’s still in use, or application logic could fail, making the router unresponsive or causing a full reboot.

Simple Example Flood (Pseudo-Code)

Here’s a Python script that demonstrates what such a resource-flooding exploit might look like—NOTE: This is a demonstration for labs only and not an exact exploit for Juniper products!

import requests
import threading

def flood_target(target_url, times):
    for _ in range(times):
        try:
            requests.get(target_url)
        except Exception as e:
            print("Error:", e)

# Example usage: Each thread makes 10,000 requests
target = "http://router.example.com/vulnerable-api";
threads = []

for _ in range(10):  # Start 10 threads
    t = threading.Thread(target=flood_target, args=(target, 10000))
    t.start()
    threads.append(t)

for t in threads:
    t.join()

A real attack against network devices would likely use low-level crafted packets rather than HTTP, but this illustrates the basic idea: hammer the interface until the counter overflows.

Mitigation and Fixes

Juniper Networks has released patches.

21.3R2-EVO or later

Workarounds:  
There are no specific configuration workarounds. Limiting exposure (e.g., management access, strong ACLs) can reduce risk.

Vendor advisory:  
- JSA11213: Junos OS Evolved: Denial of Service in kernel due to an overflow of kernel reference counters (CVE-2022-22195)

Technical Takeaways

- Reference count overflows are dangerous! They are a classic bug in C/C++ codebases.
- Even unauthenticated attackers on the same network or over the Internet can trigger such bugs if network interfaces are exposed.
- Always check for overflows when updating counters, and favor types or logic that avoid wrapping around.

References

- Juniper Security Advisory JSA11213
- NVD - CVE-2022-22195

Final Thoughts

CVE-2022-22195 is a good example of how deep inside the networking stack, one small coding mistake can have far-reaching security consequences—even allowing unauthenticated users to crash critical network devices. Patch your systems, audit your code for reference count bugs, and always keep systems isolated where possible.

Timeline

Published on: 04/14/2022 16:15:00 UTC
Last modified on: 04/21/2022 09:55:00 UTC