CVE-2024-21635 is an improper authentication vulnerability classified under CWE-287 affecting the usememos memos application, a privacy-focused, lightweight note-taking service. The core issue lies in the handling of Access Tokens used for authenticating application access. In versions up to and including 0.18.1, when a user changes their password to secure their account after a suspected compromise, the existing Access Tokens are not invalidated or revoked. This means that any attacker who previously obtained an Access Token can continue to access the victim's account despite the password change. The tokens themselves have generic descriptions, which complicates the identification and manual revocation of malicious tokens by legitimate users. The vulnerability requires no user interaction and can be exploited remotely without elevated privileges, as the attacker only needs a valid Access Token obtained prior to the password change. There is no known exploit in the wild yet, and no patched version has been released at the time of this report. The recommended security improvement is to revoke all Access Tokens upon password change, forcing re-authentication on all devices and sessions. This would invalidate tokens created under the old password, closing the window of unauthorized access. The CVSS 4.0 score of 7.1 reflects the high impact on confidentiality and integrity due to persistent unauthorized access, combined with ease of exploitation and no required user interaction.

For European organizations, this vulnerability poses a significant risk to the confidentiality and integrity of sensitive information stored within the memos application. Unauthorized persistent access could lead to data leakage, intellectual property theft, or manipulation of notes that may be used for operational or strategic purposes. Since memos is marketed as a privacy-first note-taking tool, organizations relying on it for secure internal communication or documentation may face reputational damage if breaches occur. The inability to automatically revoke tokens after password changes undermines standard incident response procedures, potentially prolonging attacker presence. This is particularly critical for sectors such as finance, healthcare, and government agencies in Europe, where data privacy regulations like GDPR impose strict requirements on data protection and breach notification. Additionally, the generic token descriptions complicate forensic investigations and timely remediation. The lack of a patch means organizations must rely on manual token management and enhanced monitoring, increasing operational overhead and risk of oversight.

Until an official patch is released, European organizations using memos should implement the following mitigations: 1) Educate users to manually review and revoke all Access Tokens associated with their accounts after any password change, despite the inconvenience. 2) Implement enhanced logging and monitoring of Access Token usage to detect anomalous or suspicious activity, such as tokens used from unusual IP addresses or devices. 3) Restrict memos access to trusted networks or VPNs to reduce exposure to unauthorized token use. 4) Encourage or enforce multi-factor authentication (MFA) at the application or infrastructure level to add an additional layer of security beyond Access Tokens. 5) Regularly audit and rotate Access Tokens proactively, even without password changes, to limit token lifespan. 6) Engage with the usememos vendor or community to track patch availability and apply updates promptly once released. 7) Consider alternative note-taking solutions with stronger session management if memos is critical and no timely fix is forthcoming. These steps go beyond generic advice by focusing on compensating controls tailored to the token management weakness and operational realities.