CVE-2024-21635 affects the usememos memos application, a privacy-focused note-taking service that authenticates users via Access Tokens. In versions up to and including 0.18.1, when a user changes their password, the system fails to invalidate existing Access Tokens. This improper authentication flaw (CWE-287) means that any previously issued tokens remain valid, allowing an attacker who has obtained a token to retain access despite a password reset. The tokens are generically described, making it difficult for users or administrators to identify and revoke malicious tokens. The vulnerability does not require user interaction or elevated privileges, and the attacker can maintain persistent access to the victim’s account, compromising confidentiality and integrity of stored notes. No official patch is currently available, so the only remediation is manual deletion of tokens by the user. The CVSS 7.1 score reflects the network attack vector, low attack complexity, no privileges or user interaction needed, and high impact on confidentiality and integrity. This flaw undermines the security model of memos by not properly tying token validity to password changes, which is a fundamental security expectation in token-based authentication systems.

For European organizations using memos, this vulnerability poses a significant risk of persistent unauthorized access to sensitive notes and data. Attackers who gain access to an account can maintain access indefinitely, even after password resets, potentially leading to data breaches, intellectual property theft, or exposure of confidential information. The inability to automatically revoke tokens increases the window of exposure and complicates incident response. Organizations relying on memos for internal communications or sensitive note-taking may face compliance risks under GDPR if personal or sensitive data is compromised. The generic token descriptions hinder quick detection and remediation, increasing operational overhead. Additionally, the lack of a patch means organizations must rely on manual controls and monitoring, which may not be feasible at scale. This vulnerability could also be exploited in targeted attacks against high-value individuals or departments within European companies, especially those in sectors like finance, legal, or government where note confidentiality is critical.

Until an official patch is released, European organizations should implement the following mitigations: 1) Educate users to manually review and revoke all Access Tokens after any password change to eliminate unauthorized sessions. 2) Implement monitoring and alerting for unusual token usage patterns or access from unfamiliar devices or locations. 3) Enforce multi-factor authentication (MFA) on memos accounts to reduce the risk of initial token compromise. 4) Limit the lifespan of Access Tokens where possible by configuring shorter expiration times if supported. 5) Encourage users to regularly audit their active tokens and remove any that are unknown or suspicious. 6) Consider isolating memos usage to less sensitive environments or restricting network access until a patch is available. 7) Engage with the usememos project or community to track patch releases and apply updates promptly. 8) Review and enhance internal incident response procedures to handle token compromise scenarios effectively.