CVE-2025-23020: 
Java vulnerability analysis and mitigation

A hash collision vulnerability was discovered in Kwik before version 0.10.1 (CVE-2025-23020). The vulnerability exists in the hash table used to manage connections, which allows remote attackers to cause a considerable CPU load on the server (a Hash DoS attack) by initiating connections with colliding Source Connection IDs (SCIDs) (QUIC Advisory).

The vulnerability stems from the implementation of hash tables used to manage QUIC connections. The hash table implementation uses weak hash functions for performance reasons, making it susceptible to hash collisions. When an attacker sends multiple connection requests with specially crafted SCIDs that collide under the target hash function, it forces the server to spend significant computational resources processing these collisions. This can result in the server experiencing a slowdown factor of up to 300x when handling just 10,000 parallel malicious connections (QUIC Advisory).

The exploitation of this vulnerability can lead to a Denial of Service condition on affected servers. Attackers can cause significant server performance degradation with minimal effort, as the server bears the computational burden of processing colliding connection IDs. This asymmetric resource consumption allows attackers to effectively stall the server by forcing it to spend the majority of its computing power on inserting and looking up colliding connection IDs (QUIC Advisory).

The vulnerability has been fixed in Kwik version 0.10.1. Users are advised to upgrade to this version or later to mitigate the risk. The fix involves implementing more secure hash table mechanisms that are resistant to hash collision attacks (QUIC Advisory).