CVE-2022-24887 is an open redirect vulnerability (CWE-601) affecting Nextcloud Talk, a video and audio conferencing application integrated into the Nextcloud self-hosted productivity platform. The vulnerability exists in versions prior to 11.3.4, 12.2.2, and 13.0.0. Specifically, when users share a Deck card within a conversation, the metaData associated with that card can be manipulated by an attacker. This manipulation allows the injection of arbitrary URLs that, when clicked by users, redirect them to untrusted external websites. This open redirect flaw can be exploited to facilitate phishing attacks, social engineering, or redirect users to malicious sites hosting malware or credential harvesting pages. The vulnerability does not require authentication or user privileges beyond the ability to share Deck cards in conversations, making it accessible to any user with sharing capabilities. There are no known workarounds, but the issue is fixed in the specified patched versions. No known exploits are currently observed in the wild. The vulnerability impacts confidentiality and integrity indirectly by enabling phishing and social engineering attacks, while availability is not directly affected. The flaw arises from insufficient validation or sanitization of URLs in the Deck card metaData, allowing redirection to arbitrary external domains.

For European organizations using Nextcloud Talk, especially those deploying versions prior to the patched releases, this vulnerability poses a moderate risk. Attackers could leverage the open redirect to craft convincing phishing campaigns targeting employees, partners, or customers, potentially leading to credential theft, unauthorized access, or malware infections. Organizations in sectors with high reliance on secure communications, such as finance, healthcare, and government, may face increased risks due to the potential for social engineering attacks exploiting this vulnerability. The self-hosted nature of Nextcloud means that organizations controlling their own instances must proactively update to mitigate exposure. The indirect nature of the impact means that while the platform itself is not compromised, the trust in communications can be undermined, leading to reputational damage and potential data breaches if phishing is successful.

1. Immediate upgrade of Nextcloud Talk to versions 11.3.4, 12.2.2, or 13.0.0 or later to apply the official patch addressing the open redirect vulnerability. 2. Implement strict URL filtering and validation on user-generated content, particularly Deck card metaData, to prevent injection of untrusted URLs. 3. Educate users to be cautious when clicking on links shared within Nextcloud Talk conversations, especially those originating from unexpected or unknown sources. 4. Deploy web security gateways or email security solutions capable of detecting and blocking phishing URLs and malicious redirects. 5. Monitor Nextcloud Talk logs for unusual sharing activity or patterns indicative of exploitation attempts. 6. For organizations unable to immediately patch, consider restricting Deck card sharing permissions to trusted users only or disabling the feature temporarily until patched. 7. Conduct regular security awareness training emphasizing the risks of open redirects and social engineering attacks.