The decode-until-stable loops in _sanitize_proxy_path (terminals.py, cap 8) and
_safe_static_redirect_path (models.py, cap 2) proceed with whatever remains after the
cap instead of rejecting it. A path encoded more times than the cap therefore exits the
loop still percent-encoded, passes the literal '..' / prefix checks (the dots are still
%2E, not '..'), and is forwarded to the upstream terminal server, or emitted as a
redirect Location, which then decodes it once more and resolves the traversal. This is
the residual of the decode-until-stable hardening added for CVE-2026-54017: the cap is a
fixed depth, not a true stability guarantee.
Reject when the value is still not stable after the cap (unquote(x) != x), so anything
encoded more deeply than the cap fails closed rather than being forwarded. Legitimate
paths stabilize within a pass or two and are unaffected.
Co-authored-by: DavidCarliez <271374756+DavidCarliez@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
