When decoding a compressed response body (gzip, deflate, br, or zstd), HTTPX2 fully decompressed each network read before yielding content to the application. A small compressed input could therefore cause a large intermediate memory allocation, even when the application streamed the response to keep memory usage bounded.
httpcore2 does not start TLS for wss:// connections routed through a SOCKS5 proxy. The WebSocket opening handshake and all subsequent frames are sent in plaintext through the proxy path, despite the caller selecting the secure wss scheme. The transport flaw affects httpcore2 releases before 2.10.0. HTTPX2 exposed this behavior through its public Client.websocket() and AsyncClient.websocket() APIs from 2.6.0 through 2.9.1.
HTTPX2's Server-Sent Events (SSE) parser repeatedly copied and rescanned buffered text when a server split one unterminated line across many response chunks. The total work grows quadratically with the length of the line. An attacker-controlled or compromised SSE endpoint can exploit this behavior to consume excessive client CPU.
HTTPX2 serializes the per-file Content-Type and custom headers supplied through the files= tuple API directly into the multipart/form-data body without validating custom header names or values. An attacker who can influence upload metadata passed to HTTPX2 can use CR or LF characters to terminate a multipart part header and inject additional part headers or end the part header block early.
HTTPX2 can automatically add a Content-Length header to a request that already contains a caller-supplied Transfer-Encoding header. The resulting HTTP/1.1 request contains both framing headers, which can create an ambiguous message boundary and enable request smuggling or connection desynchronization when processed by intermediaries that disagree about which header takes precedence.