Saint HPACK Bomb

Technical record

Disclosed on

August 3 2016

CVE

CVE-2016-6581CVE-2016-1544CVE-2016-2525

Product

nghttp2 · nghttp2

A HTTP/2 implementation built using any version of the Python HPACK library between v1.0.0 and v2.2.0 could be targeted for a denial of service attack, specifically a so-called "HPACK Bomb" attack. This attack occurs when an attacker inserts a header field that is exactly the size of the HPACK dynamic header table into the dynamic header table. The attacker can then send a header block that is simply repeated requests to expand that field in the dynamic table. This can lead to a gigantic compression ratio of 4,096 or better, meaning that 16kB of data can decompress to 64MB of data on the target machine.

Sources: imperva.com · python-hyper.org