Go · github.com/xuri/excelize/v2
Excelize: Negative shared-string index causes panic in GetCellValue and GetRows
Excelize parses shared-string cell values with strconv.Atoi and checks only the upper bound before indexing the shared string slice. If an XLSX file contains a shared-string cell with <v>-1</v>, the parsed index is negative. The upper-bound check still passes (len(sharedStrings) > -1), and Excelize indexes sharedStrings[-1], causing a runtime panic.
This was reproduced on the current default branch commit 1213a8bd7c5ab360554603ac5c995ccaf6eb4314 and the latest release tag v2.10.1 (5ad5ab3af0054c55bdce09f1530085600e9f2e45). The issue is independent from the row-bound allocation report, so I am reporting it separately.
github.com/xuri/excelize/v21213a8bd7c5ab360554603ac5c995ccaf6eb4314, and release v2.10.1An attacker who can provide an XLSX file to an application using Excelize can trigger a process panic when the application reads the malicious cell through common APIs such as GetCellValue or GetRows. In services that parse untrusted spreadsheets without a panic recovery boundary, this can cause denial of service.
For shared-string cells (t="s"), xlsxC.getValueFrom() parses the cell value as a shared-string index and only checks whether the index is below len(d.SI) before indexing:
xlsxSI, _ := strconv.Atoi(strings.TrimSpace(c.V))
if len(d.SI) > xlsxSI {
return d.SI[xlsxSI].String(), nil
}
For xlsxSI == -1, len(d.SI) > -1 is true, so the code proceeds to index d.SI[-1] and panics.
<?xml version="1.0" encoding="UTF-8"?>
<worksheet xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main">
<sheetData>
<row r="1"><c r="A1" t="s"><v>-1</v></c></row>
</sheetData>
</worksheet>
The workbook also contains a normal sharedStrings.xml with one string (ok), so the failure is specifically due to accepting a negative index.
Calling GetCellValue("Sheet1", "A1") on the workbook panics:
== negative shared string GetCellValue ==
elapsed=0s alloc_delta=0MB
PANIC: runtime.boundsError runtime error: index out of range [-1]
Calling GetRows("Sheet1") on the same workbook also panics:
== negative shared string GetRows ==
elapsed=0s alloc_delta=0MB
PANIC: runtime.boundsError runtime error: index out of range [-1]
The same results were observed on current default branch commit 1213a8bd7c5ab360554603ac5c995ccaf6eb4314 and on release v2.10.1.
Malformed shared-string indices should be rejected or treated as missing/invalid string references without panicking.
Check both lower and upper bounds before indexing the shared string table. For example:
if xlsxSI >= 0 && xlsxSI < len(d.SI) {
return d.SI[xlsxSI].String(), nil
}
Add regression tests for GetCellValue() and GetRows() on t="s" cells whose <v> value is negative.
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Check my repoSources: CISA KEV (public domain), OSV.dev & GitHub Advisory Database (CC-BY-4.0), FIRST EPSS, NVD/CWE (public domain). Served live from the Stateward advisory database.