GHSA-5h23-36rv-pm65 Excelize: GetStyle panics on a negative fillId, borderId or fontId in styles.xml

• Go github.com/xuri/excelize/v2: >= 2.8.0, < 2.11.1-0.20260731010303-ae2113b410e5 → fixed in 2.11.1-0.20260731010303-ae2113b410e5

Summary `File.GetStyle` indexes the fill, border and font tables with values taken straight out of `xl/styles.xml`, and the conditions gating those lookups check only the upper bound. A workbook whose `cellXfs` entry carries `fillId="-1"`, `borderId="-1"` or `fontId="-1"` reaches a negative slice index and panics. excelize has no `recover()`, so the panic leaves `GetStyle` and takes the calling process with it. Same defect class as GHSA-48hm-4h8j-58fg, the negative shared-string index, in a different file. That one was fixed by adding the missing lower bound; these three sites still lack it. Where it is `styles.go`, in `GetStyle`, lines 1683, 1686 and 1689: ```go xf := s.CellXfs.Xf[idx] if extractStyleCondFuncs"fill" { f.extractFills(s.Fills.Fill[*xf.FillID], s, style) } if extractStyleCondFuncs"border" { f.extractBorders(s.Borders.Border[*xf.BorderID], s, style) } if extractStyleCondFuncs"font" { style.Font = extractFont(s.Fonts.Font[*xf.FontID]) } ``` The conditions, at lines 1171 to 1185, bound only the top: ```go "fill": func(xf xlsxXf, s *xlsxStyleSheet) bool { return (xf.ApplyFill == nil || (xf.ApplyFill != nil && *xf.ApplyFill)) && xf.FillID != nil && s.Fills != nil && *xf.FillID = 0) ok style=true err= fillId=-1 PANIC: runtime error: index out of range [-1] borderId=-1 PANIC: runtime error: index out of range [-1] fontId=-1 PANIC: runtime error: index out of range [-1] ``` The control confirms the harness reads a valid file correctly, so the three panics are the negative ids rather than a broken fixture. Worth mentioning because my first attempt at this harness patched only `fillId` and appeared to show the other two were fine; they are not, the replacement had simply missed them. Impact Any application that opens an untrusted `.xlsx` and reads cell styling crashes. `GetStyle` is reached through `GetCellStyle` and from the style-copying and rendering paths, so it sits on the ordinary read path. With no `recover()` anywhere in excelize, a CLI or worker exits and a service returns 500 per request unless the caller installed its own recovery middleware. No memory corruption and no information disclosure. Availability only. Suggested fix Add the lower bound to each of the three conditions, matching what line 1677 already does for the style index: ```go *xf.FillID >= 0 && *xf.FillID < len(s.Fills.Fill) ``` and the same for `BorderID` and `FontID`. Three one-line changes in `extractStyleCondFuncs`.