fix: TOCTOU allowlist bypass + exec.cwd silently ignored - #101
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Bug #1 — TOCTOU symlink-swap allowlist bypass: handler_fs.go read/write operations used the raw p.Path instead of the canonical (symlink-resolved) path returned by checkAllowed. An attacker with filesystem write access could swap a symlink component between the allowlist check and the file operation, reading or writing files outside the permitted roots. Fix: pass canonical to Stat, ReadFile, WriteFile. Bug #2 — exec.cwd silently ignored: handler_exec.go passed the original cwd (or the shell's current cwd) to Shell.Run(callCtx, cwd, p.Command), but SessionAdapter.Run discarded the target parameter entirely. Commands ran in whatever directory the persistent bash session happened to be in. Fix: pass canonical (validated/resolved path) from handler to Shell.Run. SessionAdapter.Run now prepends when target is non-empty, so explicit cwd is honoured. Signed-off-by: Blasius Patrick <blasius.patrick@gmail.com>
Signed-off-by: Blasius Patrick <blasius.patrick@gmail.com>
Signed-off-by: Blasius Patrick <blasius.patrick@gmail.com>
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Summary
Fixes two bugs from the deep peer review of
hermes-node.Bug #1 — TOCTOU symlink-swap allowlist bypass
handler_fs.go:197,223,340used the rawp.PathforStat/ReadFile/WriteFilecalls, butcheckAllowed()returns a symlink-resolvedcanonicalpath. An attacker with filesystem write access could swap a symlink component between the allowlist check and the file operation, bypassing the allowlist.Fix: Pass
canonical(the resolved path fromcheckAllowed) instead ofp.Pathto all three file I/O operations.Bug #2 —
exec.cwdsilently ignoredSessionAdapter.Rundiscarded thetarget/cwdparameter entirely. Commands ran in whatever directory the persistent bash session happened to be in, regardless of thecwdfield in the exec payload.Fix (two parts):
handler_exec.go:249— passescanonical(the resolved, validated working directory) instead of rawcwdtoShell.Run.adapter.go—SessionAdapter.Runnow prependscd <target>when target is non-empty, so the command executes in the caller-intended directory.Build: clean. Tests: 7/7 packages pass, no races.