Some HTTP/2 implementations are vulnerable to window size manipulation and stream prioritization manipulation, potentially leading to a denial of service. The attacker requests a large amount of data from a specified resource over multiple streams. They manipulate window size and stream priority to force the server to queue the data in 1-byte chunks. Depending on how efficiently this data is queued, this can consume excess CPU, memory, or both.

sslheaders plugin extracts information from the client certificate and sets headers in the request based on the configuration of the plugin. The plugin doesn't strip the headers from the request in some scenarios. This problem was discovered in versions 6.0.0 to 6.0.3, 7.0.0 to 7.1.5, and 8.0.0 to 8.0.1.