CVE-2021-47877: GeoGebra Calculator DoS Vulnerability

CVE-2021-47877 Overview

CVE-2021-47877 is a Denial of Service vulnerability affecting GeoGebra Graphing Calculator version 6.0.631.0. The vulnerability allows attackers to crash the application by inputting an oversized buffer. Specifically, attackers can generate a payload of 8000 repeated characters to overwhelm the input field and cause the application to become unresponsive.

This vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling), indicating that the application fails to properly limit the size of input data, leading to resource exhaustion.

Critical Impact

Attackers can cause denial of service by crashing the GeoGebra Graphing Calculator application through buffer overflow in input fields, disrupting educational and mathematical workflow activities.

Affected Products

• GeoGebra Graphing Calculator version 6.0.631.0

Discovery Timeline

• 2026-01-21 - CVE CVE-2021-47877 published to NVD
• 2026-01-21 - Last updated in NVD database

Technical Details for CVE-2021-47877

Vulnerability Analysis

This vulnerability stems from improper resource allocation handling within GeoGebra Graphing Calculator. The application fails to implement adequate input validation or boundary checks when processing user-supplied data in input fields. When a user or attacker provides an excessively large input (approximately 8000 characters), the application is unable to handle the resource allocation request, resulting in application instability and eventual crash.

The local attack vector means an attacker would need local access to the system or the ability to convince a user to input the malicious payload. This could be achieved through social engineering tactics where a user is tricked into copying and pasting a crafted string into the calculator's input field.

Root Cause

The root cause is CWE-770: Allocation of Resources Without Limits or Throttling. GeoGebra Graphing Calculator does not implement proper bounds checking or input length validation on its input fields. When an oversized buffer is submitted, the application attempts to allocate resources to process the input without enforcing limits, leading to resource exhaustion and application crash.

Attack Vector

The attack requires local access (AV:L) to the vulnerable application. An attacker must craft a payload consisting of approximately 8000 repeated characters and input it into one of the application's text fields. This can be accomplished through:

1. Direct input by a local user with access to the application
2. Social engineering tactics to trick a legitimate user into pasting the malicious payload
3. Automated scripts that interact with the application's input fields

The attack does not require any special privileges (PR:N) but does require user interaction (UI:A), such as entering or pasting the payload into an input field. Successful exploitation results in high availability impact (VA:H) as the application becomes unresponsive or crashes entirely.

Technical details and proof-of-concept information can be found in the Exploit-DB #49653 advisory.

Detection Methods for CVE-2021-47877

Indicators of Compromise

• Sudden application crashes or unresponsive behavior in GeoGebra Graphing Calculator
• Unusually large clipboard contents being pasted into application input fields
• System logs indicating memory allocation failures associated with GeoGebra processes
• Repeated application restarts or user complaints about instability

Detection Strategies

• Monitor for abnormally large input strings being processed by GeoGebra Graphing Calculator
• Implement endpoint monitoring to detect application crashes and correlate with suspicious input activity
• Review application logs for memory exhaustion or buffer-related errors
• Deploy endpoint detection rules that flag applications becoming unresponsive after processing large inputs

Monitoring Recommendations

• Configure endpoint protection to monitor GeoGebra Graphing Calculator process stability
• Implement application performance monitoring to detect abnormal resource consumption
• Set up alerts for repeated application crashes that may indicate exploitation attempts
• Review the VulnCheck Advisory for GeoGebra for updated threat intelligence

How to Mitigate CVE-2021-47877

Immediate Actions Required

• Update GeoGebra Graphing Calculator to the latest available version from the GeoGebra Official Site
• Implement application whitelisting to control which applications can be executed on sensitive systems
• Educate users about the risks of copying and pasting untrusted content into applications
• Consider restricting clipboard functionality in high-security environments where this application is used

Patch Information

Users should check the official GeoGebra website for security updates addressing this vulnerability. The vendor has not published specific patch details in the available references. Organizations should upgrade to versions newer than 6.0.631.0 and verify that input validation improvements have been implemented.

Workarounds

• Restrict the use of GeoGebra Graphing Calculator version 6.0.631.0 until a patched version is available
• Implement input length restrictions at the operating system or application wrapper level if technically feasible
• Use web-based GeoGebra alternatives that may have different input handling mechanisms
• Deploy endpoint protection solutions that can detect and block denial of service attempts against desktop applications

# Check installed GeoGebra version (Windows PowerShell)
Get-ItemProperty "HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\*" | Where-Object { $_.DisplayName -like "*GeoGebra*" } | Select-Object DisplayName, DisplayVersion

# Monitor for GeoGebra process crashes (Windows Event Log)
Get-WinEvent -FilterHashtable @{LogName='Application'; ProviderName='Application Error'} | Where-Object { $_.Message -like "*GeoGebra*" }