Overview
The vulnerability, known as CVE-2023-49549, impacts Cesanta mjs 2.20.0. It allows a remote attacker to cause a denial of service attack through the mjs_getretvalpos function in the mjs.c file. This has potential wide-ranging effects, impacting the availability of services that use the Cesanta mjs and potentially leading to system compromise or data leakage.
Vulnerability Summary
CVE ID: CVE-2023-49549
Severity: High (CVSS: 7.5)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Execution of unauthorized code or instructions, potential system compromise, and data leakage.
Affected Products
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Product | Affected Versions
Cesanta mjs | 2.20.0
How the Exploit Works
A malicious actor can exploit this vulnerability by sending a specially crafted request to the target system. This request triggers a flaw in the mjs_getretvalpos function in the mjs.c file, causing an unexpected behavior in the Cesanta mjs, leading to a denial of service. The exploitation could also lead to unauthorized execution of code leading to system compromise or data leakage.
Conceptual Example Code
The following pseudocode illustrates a conceptual example of how the vulnerability might be exploited. This is a simplified representation and actual exploitation may require more complex steps.
POST /mjs_function/mjs_getretvalpos HTTP/1.1
Host: target.example.com
Content-Type: application/json
{ "malicious_payload": "specially_crafted_request" }
In the real-world scenario, the “specially_crafted_request” would be designed to trigger the vulnerability in the mjs_getretvalpos function, causing the denial of service.
Mitigation
Users are advised to apply the vendor-supplied patch to remediate this vulnerability. If the patch cannot be applied immediately, the use of a Web Application Firewall (WAF) or Intrusion Detection System (IDS) as temporary mitigation is recommended. These tools can be configured to detect and block attempts to exploit this vulnerability.

