CVE-2022-2421: Improper Type Validation vulnerability in socket.io-parser (npm)

What is CVE-2022-2421 About?

The `socket.io-parser` library (used by `socket.io` and `socket.io-client`) is vulnerable to improper type validation, allowing attackers to overwrite the `_placeholder` object. This can lead to arbitrary function references in query objects, potentially causing unexpected behavior or denial of service. The exploitation requires sending specially crafted packets and is moderately easy for an attacker familiar with Socket.IO communication.

Affected Software

socket.io-parser
- >4.0.0, <4.0.5
- <3.3.3
- >4.1.0, <4.2.1
- >3.4.0, <3.4.2

Technical Details

The vulnerability stems from improper type validation within the socket.io-parser library. Specifically, when processing incoming Socket.IO packets, a malicious user can craft a packet containing a _placeholder object with a manipulated num field. Due to insufficient validation, the socket.io-parser (and subsequently socket.io) can be tricked into interpreting values in the num field (e.g., 'push', 'hasOwnProperty') as references to functions or properties of Array or Object prototypes, rather than as expected buffer indices. This allows an attacker to inject arbitrary function references into the packet's data object, leading to potential denial of service (e.g., if a server expects a buffer but receives a function reference) or other unexpected application behavior if the application attempts to operate on these references.

What is the Impact of CVE-2022-2421?

Successful exploitation may allow attackers to inject arbitrary function references, leading to unexpected application behavior, denial of service (DoS), or potentially other impacts depending on how the application handles these injected references.

What is the Exploitability of CVE-2022-2421?

Exploitation requires sending specially crafted Socket.IO packets to a server using the vulnerable library. The complexity is moderate, requiring knowledge of the Socket.IO protocol and the ability to craft specific JSON payloads that leverage the type validation flaw. No authentication or privileged access is required to initiate the attack; it's a remote, unauthenticated attack against the message parsing component. The primary constraint is that the server must be expecting certain data types in its event handlers (e.g., Buffer objects) without performing explicit type checks. The vulnerability is significantly mitigated if the server explicitly checks incoming data types (e.g., Buffer.isBuffer(val)), otherwise, the likelihood of exploitation is higher.

What are the Known Public Exploits?

PoC Author	Link	Commentary
No known exploits

What are the Available Fixes for CVE-2022-2421?

A Fix by Resolved Security Exists!

See how we help you strengthen security with automated backported fixes for your libraries.

About the Fix from Resolved Security

The patch ensures that the _placeholder object in the packet has a numeric, valid, in-bounds num property before using it to index the attachment buffers, throwing errors for invalid or unexpected attachment numbers. It also prevents plaintext or binary data from being processed out-of-order during packet reconstruction. This directly fixes CVE-2022-2421 by preventing attacker-controlled out-of-bounds or invalid buffer access, which could otherwise lead to memory exposure or denial of service.

Available Upgrade Options

socket.io-parser
- <3.3.3 → Upgrade to 3.3.3
socket.io-parser
- >3.4.0, <3.4.2 → Upgrade to 3.4.2
socket.io-parser
- >4.0.0, <4.0.5 → Upgrade to 4.0.5
socket.io-parser
- >4.1.0, <4.2.1 → Upgrade to 4.2.1

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Additional Resources

What are Similar Vulnerabilities to CVE-2022-2421?

Similar Vulnerabilities: CVE-2020-28500 , CVE-2021-3807 , CVE-2022-25860 , CVE-2022-25912 , CVE-2021-23386

CVE-2022-2421 Improper Type Validation vulnerability in socket.io-parser (npm)