CVE-2025-29785 is a high-severity vulnerability affecting quic-go version 0.50.0, an implementation of the QUIC protocol written in Go. The vulnerability arises from the loss recovery logic for path probe packets introduced in version 0.50.0. Specifically, a malicious QUIC client can exploit this flaw by first sending valid QUIC packets from multiple remote addresses, which triggers the server's path validation logic to send path probe packets. The attacker then sends specially crafted ACK packets acknowledging the server's packets in a manner that causes a nil-pointer dereference in the quic-go server implementation. This uncaught exception results in a crash or denial of service (DoS) condition. The vulnerability is classified under CWE-248 (Uncaught Exception), indicating that the software does not properly handle an unexpected condition, leading to a runtime error. The issue was patched in version 0.50.1, which includes tests generating random sequences of sent packets (both regular and path probe packets) to ensure coverage of corner cases. No known workarounds exist, and exploitation does not require authentication or user interaction. The CVSS v3.1 base score is 7.5, reflecting a network attack vector with low attack complexity, no privileges required, no user interaction, and a high impact on availability but no impact on confidentiality or integrity. No known exploits are currently observed in the wild.

For European organizations, this vulnerability poses a significant risk primarily to services and applications that utilize quic-go version 0.50.0 for QUIC protocol communication. Since QUIC is increasingly used to improve web performance and security, particularly in HTTP/3 implementations, affected servers could be forced into denial of service by remote attackers, leading to service outages and degraded user experience. This can impact critical web services, APIs, and real-time communication platforms relying on quic-go. The availability disruption could affect e-commerce, financial services, healthcare, and government portals, potentially causing operational downtime and reputational damage. Given the lack of known workarounds, organizations must prioritize patching. The vulnerability does not directly expose data confidentiality or integrity but can be leveraged as part of a broader attack strategy to disrupt services or as a vector for further exploitation if combined with other vulnerabilities.

European organizations should immediately identify any deployments of quic-go version 0.50.0 within their infrastructure, including embedded systems, microservices, and cloud-native applications. The primary mitigation is to upgrade to quic-go version 0.50.1 or later, which contains the patch addressing this vulnerability. Since no workarounds exist, patching is critical. Organizations should also implement network-level protections such as rate limiting and anomaly detection to identify unusual patterns of QUIC traffic, especially from multiple remote addresses that could indicate attempts to trigger path validation logic. Monitoring logs for unexpected crashes or exceptions in services using quic-go can help detect exploitation attempts. Additionally, applying strict ingress filtering and employing Web Application Firewalls (WAFs) capable of inspecting QUIC traffic may reduce exposure. For critical services, consider deploying redundancy and failover mechanisms to mitigate potential downtime caused by exploitation attempts.