AIKIDO-2026-991372

TL;DR

Uint::overflowing_shl and overflowing_shr in the ruint crate returned false-negative overflow flags. Left shifts missed bits shifted above BITS but still inside the top limb (non-limb-aligned widths such as U160) and limbs wholly discarded by shifts of 64 or more; right shifts missed wholly discarded low limbs. The shifted value itself was correct, but the wrong flag propagates to checked_*, strict_*, and saturating_* shift helpers. On no-alloc builds, the incorrect checked_shl result causes to_base_be (and string formatting) to loop forever for non-limb-aligned widths, enabling denial of service when formatting is reachable from untrusted input. Separately, wrapping_shl/wrapping_shr on 64/128/256-bit types truncated the shift amount modulo 2^32, so shifts of 2^32 or more returned an incorrectly wrapped value instead of zero.