The link in the HN submission contains the same text and excerpt from your link.

Additionally they note: -

"While exploitability to remote code execution depends on platform and toolchain mitigations, the stack-based write primitive represents a severe risk."

IMO, probably in of itself, this alone is not able to do much besides maybe a crash / Denial of Service on modern systems. But it might be able to be used as part of a more advanced exploit chain, alongside other vulnerabilities, to potentially reach remote code execution, though this would be a much more sophisticated exploit and is maybe a bit of a reach. Still, I hesitate to call it impossible on modern systems due to the creativity of exploit developers.

"Modern platform" is doing a lot of lifting; CMS and PKCS#7 rear their heads in all kinds of random places, like encryption/signing of OTA updates for routers. Those platforms are often (unreasonably) 10-20 years behind the norm for compile-time mitigations.