Improper Neutralization of Formula Elements in a CSV File

The software saves user-provided information into a Comma-Separated Value (CSV) file, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as a command when the file is opened by spreadsheet software.


Description

User-provided data is often saved to traditional databases. This data can be exported to a CSV file, which allows users to read the data using spreadsheet software such as Excel, Numbers, or Calc. This software interprets entries beginning with '=' as formulas, which are then executed by the spreadsheet software. The software's formula language often allows methods to access hyperlinks or the local command line, and frequently allows enough characters to invoke an entire script. Attackers can populate data fields which, when saved to a CSV file, may attempt information exfiltration or other malicious activity when automatically executed by the spreadsheet software.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

Hyperlinks or other commands can be executed when a cell begins with the formula identifier, '='

=HYPERLINK(link_location, [friendly_name])

Stripping the leading equals sign, or simply not executing formulas from untrusted sources, impedes malicious activity.

HYPERLINK(link_location, [friendly_name])

See Also

Data Neutralization Issues

Weaknesses in this category are related to the creation or neutralization of data using an incorrect format.

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses without Software Fault Patterns

CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.


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