CVE-2023-33953: 
Python vulnerability analysis and mitigation

gRPC contains a vulnerability that allows HPACK table accounting errors which could lead to unwanted disconnects between clients and servers. The vulnerability, identified as CVE-2023-33953, was disclosed on August 9, 2023, affecting multiple versions of gRPC including versions up to 1.53.2, 1.54.0-1.54.3, 1.55.0-1.55.2, and 1.56.0-1.56.2 (NVD).

The vulnerability encompasses three distinct attack vectors related to HPACK parsing: unbounded memory buffering and unbounded CPU consumption. The CPU consumption issue stems from a copy operation occurring per-input-block in the parser, resulting in an O(n^2) parsing loop where n is controlled by the client. The memory buffering issues include: header size limit check occurring after string reading (allowing up to 4GB string buffering before rejection), infinite zero padding in HPACK varints requiring complete parsing, and per-frame metadata overflow checking enabling infinite buffering through sequential frames. The vulnerability has received a CVSS v3.1 Base Score of 7.5 (HIGH) (NVD).

The vulnerability can lead to denial of service conditions through two primary mechanisms: unbounded memory buffering in the HPACK parser and unbounded CPU consumption. This can result in resource exhaustion and unwanted disconnections between clients and servers in exceptional cases (NVD).

Updates have been released to address this vulnerability. Users should upgrade to gRPC version 1.53.2 or later, 1.54.3 or later, 1.55.2 or later, or 1.56.2 or later, depending on their current version track (NVD).