Excelize is a Go language library for reading and writing Microsoft Excel spreadsheets. From 2.3.1 to 2.11.0, the decryption dispatch performs insufficient structural and parameter validation before standard and agile decryptors slice, index, allocate, and divide using attacker-controlled values. Decrypt passes attacker-controlled EncryptionInfo and EncryptedPackage data into standardDecrypt or agileDecrypt before validating the structures used by those routines. When a malformed OLE compound file with a version-valid EncryptionInfo stream is opened or passed to Decrypt, nine malformed-input classes reach unrecovered Go runtime panics instead of the documented error path, allowing an attacker to terminate the calling process. No fixed version is available as of this review.

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

### Summary

Any file whose first 8 bytes are the OLE compound-file signature (`D0 CF 11 E0 A1 B1 1A E1`) is routed by `OpenFile`/`OpenReader`/`OpenBytes` → `openReaderAt` → `Decrypt`. The version dispatch only guarantees `len(EncryptionInfo) >= 4` before handing attacker-controlled `EncryptionInfo`/`EncryptedPackage` buffers to `standardDecrypt`/`agileDecrypt`, and no callee validates structure. Malformed but version-valid content therefore fails as an **unrecovered runtime panic** instead of an error, terminating the calling process.

### Details

All panic classes below were execution-confirmed against pristine master (`ecd99d761fe0`, 2026-09-08). `excelize.go:211-213` maps `Decrypt` *errors* to `ErrWorkbookFileFormat`, but panics bypass that path and kill the process.

| # | Malformed input | Panic | Site | |---|---|---|---| | 1 | standard, `len(EncryptionInfo)` 4–11 | slice bounds `[:12]` | `crypt.go:238` | | 2 | standard, attacker-controlled `headerSize` uint32 | slice bounds `[12:12+headerSize]` / fixed-offset header reads | `crypt.go:238-249` | | 3 | standard, verifier remainder < 72 (AES) / 60 (RC4) bytes | slice bounds in `standardEncryptionVerifier` | `crypt.go:282-295` | | 4 | standard, `header.KeySize` = 0xFFFFFFFF | slice bounds `[:536870911]` with capacity 48 | `crypt.go:321` | | 5 | standard, `EncryptedPackage` stream missing/short | slice bounds `[8:0]` | `crypt.go:268` | | 6 | agile, `len(EncryptionInfo)` 4–7 | slice bounds `[8:4]` | `crypt.go:407` | | 7 |…