chunkloris: net/http (stdlib)

part of the chunkloris per-chunk amplification survey. this page is the per-server record for net/http (stdlib) under http/1.1 chunked transfer encoding.

at a glance

server: net/http (stdlib) go-1.23.12
runtime: go-1.23
ecosystem: go
concurrency model: n-m-scheduler
parser: Go stdlib chunked decoder (net/http/internal/chunked.go)
delivery granularity: per-chunk
chunk-limit helper: none exposed by the framework
verdict: per-chunk — the parser/dispatcher boundary delivers one event per wire chunk. cpu cost under paced mode b is measurable per chunk.
scaling exponent (mode a): 0.92 (wall time vs N, log-log slope across common cells)
scaling exponent (mode b): 1.00

measurements

all cells run on a 1-vcpu docker container. cpu cost is derived from the target container’s cgroup v2 cpu.stat usage_usec delta around each cell.

mode	N	wall (s)	server cpu %	µs / chunk	basis	ok
`A-bridge-coalesced`	50,000	0.002	1516.8	0.644	server-cpu-cgroup	✓
`A-bridge-coalesced`	100,000	0.003	959.5	0.315	server-cpu-cgroup	✓
`A-bridge-coalesced`	250,000	0.009	461.8	0.168	server-cpu-cgroup	✓
`B-paced-100us`	50,000	5.125	11.2	11.482	server-cpu-cgroup	✓
`B-paced-100us`	100,000	10.242	8.2	8.381	server-cpu-cgroup	✓
`B-paced-100us`	250,000	25.603	7.8	7.992	server-cpu-cgroup	✓

what this means

the parser/dispatcher path on this server delivers one event per chunked-transfer-encoding chunk, so an attacker who sends a body as N one-byte chunks consumes roughly N × (mode-b µs/chunk) of server cpu on a single core. amplification scales linearly with N until the framework’s max_request_body_size (or equivalent) is hit.

what to do today

if this server runs as an origin behind nginx with the default proxy_request_buffering on, the per-chunk attack shape does not reach this server — nginx delivers one content-length-framed body to the upstream in a single recv().
if deployed direct-exposed, behind haproxy with default streaming, or behind any reverse proxy with proxy_request_buffering off, the per-chunk cost reaches this server.
there is no framework-level chunk-count limit in the default config; use a frontend buffer, transport-layer rate limiting, or a wrapping middleware that imposes a chunk-count cap before draining the body.

reproducer

the full reproducer for this server is in the paper repo. the docker container pins net/http (stdlib) go-1.23.12 and constrains the test container to a single cpu (--cpus=1). the prober script implements mode a (bridge-coalesced) and mode b (paced 100 µs) per the methodology section.

see the draft pdf for the full per-framework discussion.