Maven · org.http4s:http4s-blaze-server_2.12
blaze: Unbounded WebSocket message aggregation in http4s-blaze-server
http4s-blaze-server aggregates the fragments of an incoming WebSocket
message with no limit on total size or fragment count. A client that
completes a WebSocket handshake can send an unterminated fragmented
message and drive unbounded heap growth in the server JVM, resulting in
denial of service via OutOfMemoryError.
Any http4s application serving WebSocket routes over
BlazeServerBuilder is affected; no non-default configuration is required,
and maxWebSocketBufferSize does not bound the aggregate (it bounds only
individual frames). A single connection sending continuation frames that
never set FIN forces the server to buffer every fragment until the heap is
exhausted, terminating the JVM with OutOfMemoryError on the blaze
selector thread. Small fragments amplify the cost through per-frame object
overhead, so a modest volume of wire bytes is sufficient. Where the
WebSocket endpoint is reachable without authentication the attacker is
unauthenticated and remote; where the handshake requires a principal, any
authenticated client can still trigger it.
maxWebSocketBufferSize
is not a mitigation.Is your project exposed to this? Stateward checks every dependency on every pull request and flags it only if your code actually reaches it.
Check my repoSources: CISA KEV (public domain), OSV.dev & GitHub Advisory Database (CC-BY-4.0), FIRST EPSS, NVD/CWE (public domain). Served live from the Stateward advisory database.