Excelize is a Go language library for reading and writing Microsoft Excel spreadsheets. From 2.1.0 to 2.11.0, flatCols expands file-loaded column ranges without validating Min and Max against the worksheet column limit. SetColWidth reaches flatCols, which expands xlsxCol.Min through xlsxCol.Max without enforcing MaxColumns. When a crafted worksheet supplies an oversized col max attribute and the application invokes a column mutator, flatCols performs a deep copy and append for every attacker-selected column number, allowing an attacker to consume excessive CPU and memory or trigger OOM. No fixed version is available as of this review.

Affected: Go: github.com/xuri/excelize/v2

### Summary

The `max` attribute of a `<col>` element in `xl/worksheets/sheetN.xml` is read verbatim on open with no check against `MaxColumns`, and `flatCols()` then walks `Min..Max` doing a `deepcopy.Copy` and `append` per iteration. Executed: `max="300000"`, only about 18x past the real 16384 limit, cost 46.2 s of CPU and 122 MB on a single `SetColWidth` call, and the growth is linear in `max` up to 2^31-1.

Confirmed at `ae2113b` (HEAD at the time of audit).

### Details

`col.go:547`, `flatCols()`, with the two loops at `:549` and `:564`:

```go for i := col.Min; i <= col.Max; i++ { ... for i := column.Min; i <= column.Max; i++ { ... fc = append(fc, deepcopy.Copy(...)) } ```

`column.Min` and `column.Max` are plain int attributes on `xmlWorksheet.go:279-280`, bound straight from the file. `MaxColumns` is 16384 (`templates.go:176`) and nothing in the parse path compares against it.

The contrast that makes this an oversight rather than a design decision is inside the callers themselves. `SetColWidth` validates its own column argument through `parseColRange`, which clamps to `MaxColumns`. But `flatCols` iterates `ws.Cols.Col`, the file-loaded slice, so the caller's validated argument never constrains the loop. The crafted column expands no matter which column the caller touches.

The row axis has the guard this axis is missing: GHSA-h69g-9hx6-f3v4 capped `checkSheet`'s row allocation at `TotalRows`, and GHSA-q5j5-6p94-4gwc capped streaming `Rows.Next`. There is no column-…