@fastly/js-compute has a use-after-free in some host call implementations

Impact

The implementation of the following functions were determined to include a use-after-free bug:

• FetchEvent.client.tlsCipherOpensslName
• FetchEvent.client.tlsProtocol
• FetchEvent.client.tlsClientCertificate
• FetchEvent.client.tlsJA3MD5
• FetchEvent.client.tlsClientHello
• CacheEntry.prototype.userMetadata of the fastly:cache subsystem
• Device.lookup of the fastly:device subsystem

This bug could allow for an unintended data leak if the result of the preceding functions were sent anywhere else, and often results in a Compute service crash causing an HTTP 500 error to be returned. As all requests to Compute are isolated from one another, the only data at risk is data present for a single request.

Patches

This bug has been fixed in version 3.16.0 of the @fastly/js-compute package.

Workarounds

There are no workarounds for this bug, any use of the affected functions introduces the possibility of a data leak or crash in guest code.