PYSEC-2026-3847 HTTPX2: Quadratic SSE line buffering can cause CPU denial of service

Summary 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...

GHSA-F2FP-RGF2-35CP HTTPX2: Quadratic SSE line buffering can cause CPU denial of service

Summary 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...