CVE-2021-47944: memono Notepad 4.2 DOS Vulnerability

CVE-2021-47944 Overview

CVE-2021-47944 is a denial of service vulnerability in memono Notepad 4.2 for iOS. The application crashes when an attacker pastes excessively long character buffers into note fields. A payload containing 350,000 repeated characters, when pasted twice into a new note, reliably triggers an application crash. The vulnerability is classified under [CWE-789] (Memory Allocation with Excessive Size Value) and affects availability of the application on iOS devices.

Critical Impact

Attackers can crash the memono Notepad application on iOS devices by submitting oversized character buffers, resulting in loss of availability and potential data loss for unsaved notes.

Affected Products

• memono Notepad 4.2 for iOS

Discovery Timeline

• 2026-05-10 - CVE-2021-47944 published to NVD
• 2026-05-13 - Last updated in NVD database

Technical Details for CVE-2021-47944

Vulnerability Analysis

The vulnerability in memono Notepad 4.2 stems from improper handling of large input buffers in note fields. The application fails to validate or constrain the size of pasted character data before processing. When an attacker pastes a buffer containing 350,000 repeated characters twice into a new note, the application exhausts allocated memory resources and crashes.

This behavior corresponds to [CWE-789], which describes memory allocation driven by an attacker-controlled size value without proper bounds enforcement. The flaw resides entirely within input processing logic for the note editor component.

Root Cause

The root cause is the absence of length validation on user-supplied text input. The application allocates memory proportional to pasted buffer size without imposing maximum limits. iOS memory pressure handlers terminate the process once allocation thresholds are exceeded.

Attack Vector

Exploitation requires an attacker to deliver a crafted payload to a user, who then pastes the content into a memono note field. The attack does not require authentication or elevated privileges. Impact is limited to denial of service against the application itself, with no observed confidentiality or integrity consequences.

Technical details and proof-of-concept code are documented in Exploit-DB #49977 and the VulnCheck Advisory.

Detection Methods for CVE-2021-47944

Indicators of Compromise

• Repeated unexpected crashes of the memono Notepad application on iOS devices
• iOS crash reports referencing memory allocation failures or out-of-memory termination tied to the memono process
• Note files containing unusually large blocks of repeated single characters

Detection Strategies

• Review iOS device crash logs for entries referencing memono Notepad and excessive memory consumption
• Monitor mobile device management (MDM) telemetry for repeated application terminations on devices with memono installed
• Inspect synced note content for payloads consisting of long sequences of repeated characters

Monitoring Recommendations

• Enable iOS diagnostic and usage data reporting to capture crash signatures for affected devices
• Correlate user-reported application crashes with timestamps of clipboard activity where feasible
• Track installation prevalence of memono Notepad 4.2 across managed iOS fleets to scope exposure

How to Mitigate CVE-2021-47944

Immediate Actions Required

• Inventory iOS devices in the environment running memono Notepad 4.2 and identify business reliance on the application
• Advise users to avoid pasting untrusted content into memono note fields until a vendor fix is available
• Consider uninstalling memono Notepad 4.2 on managed devices where alternative note applications are acceptable

Patch Information

No vendor patch is referenced in the available advisories. Consult the VulnCheck Advisory for the latest vendor status and any updates to memono Notepad beyond version 4.2.

Workarounds

• Restrict clipboard sharing between untrusted sources and memono Notepad through iOS clipboard management controls
• Migrate sensitive note-taking workflows to an alternative iOS application until a fixed version is released
• Educate users to recognize and discard suspicious text payloads containing long repeated character sequences