GHSA-cmr8-5w4c-44v8 Fastly Compute@Edge JS Runtime has fixed random number seed during compilation

• npm @fastly/js-compute: >= 0.4.0, < 0.5.3 → fixed in 0.5.3

Impact `Math.random` and `crypto.getRandomValues` methods failed to use sufficiently random values. The initial value to seed the CSPRNG (cryptographically secure pseudorandom number generator) was baked-in to the final WebAssembly module meaning the sequence of numbers generated was predictable for that specific WebAssembly module. An attacker with access to that same WebAssembly module that calls the affected methods could use the fixed seed to predict random numbers generated by these functions. This information could be used to bypass cryptographic security controls, for example to disclose sensitive data encrypted by functions that use these generators. Patches The problem has been fixed in version 0.5.3. Corrected `Math.random` and `crypto.getRandomValues` methods to always use sufficiently random values. The previous versions would use a CSPRNG (cryptographically secure pseudorandom number generator) which we would seed with a random value. However, due to our use of Wizer, the initial value to seed the CSPRNG was baked-in to the final WebAssembly module meaning the sequence of numbers generated was predictable for that specific WebAssembly module. The new implementations of both Math.random and `crypto.getRandomValues` do not use a CSPRNG and instead pull random values from WASI (WebAssembly System Interface) libc’s random_get function, which is always a sufficiently random value. Workarounds There are no workarounds, you must upgrade to version 0.5.3 or later.