CVE-2023-49803: @koa/cors npm provides Cross-Origin Resource Sharing (CORS) for koa, a web framework for Node.js. Prior to version 5.0.0, the middleware operates in a...

Description

@koa/cors npm provides Cross-Origin Resource Sharing (CORS) for koa, a web framework for Node.js. Prior to version 5.0.0, the middleware operates in a way that if an allowed origin is not provided, it will return an `Access-Control-Allow-Origin` header with the value of the origin from the request. This behavior completely disables one of the most crucial elements of browsers - the Same Origin Policy (SOP), this could cause a very serious security threat to the users of this middleware. If such behavior is expected, for instance, when middleware is used exclusively for prototypes and not for production applications, it should be heavily emphasized in the documentation along with an indication of the risks associated with such behavior, as many users may not be aware of it. Version 5.0.0 fixes this vulnerability.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS Probability

0.28%

19.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Koajs	Cross-Origin Resource Sharing For Koa	< 5.0.0

References

Timeline

Published: Dec 11, 2023
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2023-49803?

@koa/cors npm provides Cross-Origin Resource Sharing (CORS) for koa, a web framework for Node.js. Prior to version 5.0.0, the middleware operates in a way that if an allowed origin is not provided, it will return an `Access-Control-Allow-Origin` header with the value of the origin from the request. This behavior completely disables one of the most crucial elements of browsers - the Same Origin Policy (SOP), this could cause a very serious security threat to the users of this middleware. If such behavior is expected, for instance, when middleware is used exclusively for prototypes and not for production applications, it should be heavily emphasized in the documentation along with an indication of the risks associated with such behavior, as many users may not be aware of it. Version 5.0.0 fixes this vulnerability.

How severe is CVE-2023-49803?

CVE-2023-49803 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.28% probability of exploitation in the next 30 days.

How do I fix CVE-2023-49803?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.