CVE-2026-69202: Http4s Ember HTTP/2: unbounded inbound body buffering
Ember’s HTTP/2 stack replenishes the inbound flow-control window based on bytes received off the wire, not bytes consumed by the application. Received DATA is buffered in an unbounded per-stream channel. Flow control therefore provides no backpressure: a peer can stream a large or unbounded body faster than the application drains it and the connection retains every payload in heap.
This is the read-path mirror of the outbound queue issue.
This affects an Ember receiving a request body and an Ember client receiving a response body from a hostile server.
References
- github.com/advisories/GHSA-6m4x-pp6q-5jmm
- github.com/http4s/http4s/commit/22d2335975d02dc9fb9fb75cfe002279521d86ac
- github.com/http4s/http4s/releases/tag/v0.23.35
- github.com/http4s/http4s/releases/tag/v1.0.0-M47
- github.com/http4s/http4s/security/advisories/GHSA-6m4x-pp6q-5jmm
- nvd.nist.gov/vuln/detail/CVE-2026-69202
Code Behaviors & Features
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