GHSA-563q-j3cm-6jxm Netty susceptible to HTTP/2 Reset Attack with different on-the-wire signature

• Maven io.netty:netty-codec-http2: >= 4.2.0.Final, < 4.2.15.Final → fixed in 4.2.15.Final • Maven io.netty:netty-codec-http2: < 4.1.135.Final → fixed in 4.1.135.Final

Summary Netty HTTP/2 max header size handling produces attack similar to HTTP/2 Rapid Reset. Details There is a setting in the http2 specification called `SETTINGS_MAX_HEADER_LIST_SIZE`. According to the RFC: “This advisory setting informs a peer of the maximum field section size that the sender is prepared to accept, in units of octets.” When a client sends that setting to Netty, it appears that Netty will behave as follows: • Read the request • Proxy the request to the origin • Attempt to produce a response • Create an exception while writing the headers for the response Functionally, this should be similar to the http2 reset attack, but with a different on-the-wire signature. Remediation When speaking with clients, Netty should potentially treat this as “advisory” and ignore it. It would be best to ignore the SETTINGS_MAX_HEADER_LIST_SIZE setting from clients (or ignore it when sending to clients). According to the spec, a server does not need to honor this advisory setting, and it appears that other http/2 implementations ignore it when acting as a server. Impact This is a DDoS attack similar to the HTTP/2 Rapid Reset Attack. Credit Jonathan Looney (Engineering, Netflix) Contact Ashley Tolbert (Security, Netflix) - [email protected]