Use of Insufficiently Random Values in undici

Impact

Undici fetch() uses Math.random() to choose the boundary for a multipart/form-data request. It is known that the output of Math.random() can be predicted if several of its generated values are known.

If there is a mechanism in an app that sends multipart requests to an attacker-controlled website, they can use this to leak the necessary values. Therefore, An attacker can tamper with the requests going to the backend APIs if certain conditions are met.

Patches

This is fixed in 5.28.5; 6.21.1; 7.2.3.

Workarounds

Do not issue multipart requests to attacker controlled servers.

References

• https://hackerone.com/reports/2913312
• https://blog.securityevaluators.com/hacking-the-javascript-lottery-80cc437e3b7f