New objects created without an explicit security descriptor take
their DACL from the token's default DACL, which CreateRestrictedToken
builds from the user's ambient SIDs — none of them a restricting SID.
Confined children therefore failed the write pass-2 check when
creating anonymous pipes (CreatePipe: ERROR_ACCESS_DENIED, surfaced
as Node EPERM), breaking PowerShell pipelines and other CreatePipe
consumers. Merge a full-access write-SID ACE (Everyone under
read-only) into the token default DACL at init via
SetTokenInformation(TokenDefaultDacl).
Named pipes are EXEMPT: their default security descriptor is the
kernel's PUBLIC template (owner/SYSTEM/Admins full, Everyone
read-only), which no token change influences, so libuv's piped stdio
capture stays denied for confined grandchildren — the POC-documented
boundary, now pinned by the runner suite (inherit/ignore OK, pipe
DENIED) and documented in the README pair. The NUL paragraph is
corrected to the measured matrix (Everyone has 0x1201BF on the
device: cmd/node writes land; Set-Content fails at the PS layer).
Huanqi Cao
01a3b454f6