Package Instance

Connection confusion in gRPC
When gRPC HTTP2 stack raised a header size exceeded error, it skipped parsing the rest of the HPACK frame. This caused any HPACK table mutations to also be skipped, resulting in a desynchronization of HPACK tables between sender and receiver. If leveraged, say, between a proxy and a backend, this could lead to requests from the proxy being interpreted as containing headers from different proxy clients - leading to an information leak that can be used for privilege escalation or data exfiltration.

Excessive Iteration in gRPC
gRPC contains a vulnerability that allows hpack table accounting errors could lead to unwanted disconnects between clients and servers in exceptional cases/ Three vectors were found that allow the following DOS attacks:

- Unbounded memory buffering in the HPACK parser
- Unbounded CPU consumption in the HPACK parser

The unbounded CPU consumption is down to a copy that occurred per-input-block in the parser, and because that could be unbounded due to the memory copy bug we end up with an O(n^2) parsing loop, with n selected by the client.

The unbounded memory buffering bugs:

- The header size limit check was behind the string reading code, so we needed to first buffer up to a 4 gigabyte string before rejecting it as longer than 8 or 16kb.
- HPACK varints have an encoding quirk whereby an infinite number of 0’s can be added at the start of an integer. gRPC’s hpack parser needed to read all of them before concluding a parse.
- gRPC’s metadata overflow check was performed per frame, so that the following sequence of frames could cause infinite buffering: HEADERS: containing a: 1 CONTINUATION: containing a: 2 CONTINUATION: containing a: 3 etc…

gRPC Reachable Assertion issue
There exists an vulnerability causing an abort() to be called in gRPC.
The following headers cause gRPC's C++ implementation to abort() when called via http2:

te: x (x != trailers)

:scheme: x (x != http, https)

grpclb_client_stats: x (x == anything)

On top of sending one of those headers, a later header must be sent that gets the total header size past 8KB. We recommend upgrading past git commit 2485fa94bd8a723e5c977d55a3ce10b301b437f8 or v1.53 and above.