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CVE-2026-52885 affects Notepad++ prior to version 8.9.6.4. In NppCommands.cpp, the application validates the HMAC of the on-disk shortcuts.xml only when a user command is invoked. However, the command payload that is actually executed is not read from disk at that time; it is taken from the in-memory _userCommands vector populated at application startup and never re-synchronized with the file. This creates a time-of-check to time-of-use inconsistency: an attacker with write access to shortcuts.xml can place a malicious shortcuts.xml before Notepad++ starts so the malicious command is loaded into memory, then restore a legitimate shortcuts.xml on disk before the command is triggered. When the user command fires, the HMAC check is performed against the restored benign file and succeeds, while the malicious command already resident in memory is executed.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
This repository is a small, focused local exploit PoC for CVE-2026-52885 affecting Notepad++ v8.9.6.2 on Windows. It contains two files: a README documenting the vulnerability, root cause, attack timeline, and patch analysis; and a single PowerShell exploit script, poc_8962_toctou.ps1, which operationalizes the issue. The vulnerability is a TOCTOU flaw in Notepad++'s HMAC protection for shortcuts.xml. At trigger time, Notepad++ validates the current on-disk shortcuts.xml against an HMAC stored in config.xml, but the command it executes comes from the in-memory _userCommands list loaded earlier at startup. Because these sources are not synchronized, an attacker with write access to shortcuts.xml can place a malicious UserDefinedCommands entry before launch, let Notepad++ parse it into memory, restore the legitimate file on disk, and then trigger the command. The HMAC check passes against the restored disk file while the stale malicious in-memory command still executes. The PowerShell PoC demonstrates this exact sequence. It backs up shortcuts.xml, writes a malicious XML payload containing a UserDefinedCommands entry that runs calc.exe, launches Notepad++, waits for initialization, restores the original shortcuts.xml, computes and displays the disk HMAC using MachineGuid from HKLM\SOFTWARE\Microsoft\Cryptography, extracts the expected HMAC from config.xml, and then uses user32.dll APIs to bring the Notepad++ window to the foreground and send WM_COMMAND(21000), corresponding to ID_USER_CMD+0. Finally, it checks whether calc.exe or CalculatorApp started to confirm exploitation. This is a real exploit rather than a detector: it modifies target files, triggers the vulnerable code path, and achieves attacker-controlled command execution as the current user. It is local-only, requires specific target state and file write access, and uses a hardcoded demonstration payload (calc.exe), making it best classified as OPERATIONAL rather than weaponized.
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