CVE-2025-68475 identifies a Regular Expression Denial of Service (ReDoS) vulnerability in the Fedify library, a TypeScript framework designed for building federated server applications powered by the ActivityPub protocol. The vulnerability is located in the document loader component, specifically in an HTML parsing regular expression defined at packages/fedify/src/runtime/docloader.ts:259. This regex contains nested quantifiers, a pattern known to cause catastrophic backtracking when processing specially crafted input. An attacker can exploit this by sending malicious HTML responses that trigger excessive backtracking, leading to high CPU utilization and effectively causing a denial of service. The vulnerability affects multiple versions of Fedify: all versions prior to 1.6.13, versions from 1.7.0 up to but not including 1.7.14, versions from 1.8.0 up to but not including 1.8.15, and versions from 1.9.0 up to but not including 1.9.2. The issue has been patched in these respective versions. The CVSS v3.1 base score is 7.5, reflecting a high severity due to the vulnerability's network attack vector, no required privileges or user interaction, and impact on availability only. There are no known exploits in the wild at the time of publication. The vulnerability is categorized under CWE-1333, which relates to inefficient regular expression complexity leading to denial of service. Given Fedify’s role in federated server apps, exploitation could disrupt services relying on ActivityPub federation, impacting availability and potentially causing cascading effects in federated networks.

For European organizations, the primary impact of CVE-2025-68475 is the potential for denial of service attacks against federated server applications built with vulnerable versions of Fedify. This can result in service outages, degraded performance, and disruption of federated communication channels, which are increasingly used in decentralized social networking and collaboration platforms. Organizations relying on ActivityPub-based services for internal or external communication, content sharing, or social networking could experience operational interruptions. The impact is particularly significant for entities promoting open, federated platforms such as universities, research institutions, media outlets, and privacy-focused social networks prevalent in Europe. Additionally, denial of service conditions could be leveraged as part of multi-stage attacks or to distract from other malicious activities. Although no confidentiality or integrity impacts are indicated, availability degradation can affect user trust and service reliability. The lack of required authentication or user interaction lowers the barrier for attackers to exploit this vulnerability remotely over the network, increasing risk exposure.

European organizations should immediately audit their use of the Fedify library within federated server applications and identify any deployments running vulnerable versions. The primary mitigation is to upgrade Fedify to the patched versions 1.6.13, 1.7.14, 1.8.15, or 1.9.2 or later, depending on the version branch in use. Where immediate upgrading is not feasible, organizations should implement network-level protections such as rate limiting and input validation to detect and block suspiciously large or malformed HTML responses that could trigger the ReDoS condition. Monitoring CPU usage and application logs for signs of excessive backtracking or performance degradation can provide early warning of exploitation attempts. Developers should review and refactor any custom regular expressions in their ActivityPub implementations to avoid nested quantifiers or other inefficient patterns. Employing Web Application Firewalls (WAFs) with rules targeting ReDoS attack signatures may provide additional defense. Finally, organizations should maintain an incident response plan to quickly address denial of service incidents affecting federated services.