CVE-2023-33953 Denial-of-Service in gRPC

2023-08-0912:54:47

CWE-789

CWE-834

Google

www.cve.org

grpc

vulnerability

unbounded memory

cpu consumption

unwanted disconnects

CVSS3

7.5

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

AI Score

7.9

Confidence

High

EPSS

0.001

Percentile

32.9%

JSON

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…

CNA Affected

[
  {
    "defaultStatus": "unaffected",
    "product": "gRPC",
    "vendor": "Google",
    "versions": [
      {
        "lessThan": "1.56.1",
        "status": "affected",
        "version": "0",
        "versionType": "custom"
      }
    ]
  }
]