---
id: CVE-2026-78048
title: >-
  Apache bRPC: Remote Denial of Service via Out-of-Bounds Dynamic Table Sizing
  in HPACK Decoder
summary: >-
  A reachable-assertion flaw in the HPACK header-compression decoder of the
  HTTP/2 (h2/gRPC) stack in Apache bRPC (version < 1.18.0) on all platforms
  allows a remote attacker to crash the server process by sending a crafted
  sequence of HPA…
severity: none
cwe:
  - CWE-617
vendor: Apache Software Foundation
product: apache/brpc
affected:
  - apache/brpc < 1.18.0
published: '2026-10-21'
updated: '2026-10-21'
sourceUpdated: '2026-10-21T11:51:58.752Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-78048'
references:
  - url: 'https://lists.apache.org/thread/2pf15ojj0vr7rtx95677kgtl1mx3gdgb'
tags:
  - cve.org
ingestedAt: '2026-10-21T12:48:53.763Z'
---

## Overview

A reachable-assertion flaw in the HPACK header-compression decoder of the HTTP/2 (h2/gRPC) stack in Apache bRPC (version < 1.18.0) on all platforms allows a remote attacker to crash the server process by sending a crafted sequence of HPACK headers, resulting in a denial of service.

Root Cause:
In src/brpc/details/hpack.cpp, IndexTable::Init sizes the dynamic-table ring buffer as num_headers = max_size / (32 + 2), i.e. it assumes a minimum table entry of 34 bytes (name >= 1 byte + value >= 1 byte + 32 bytes of overhead). However, RFC 7541 section 4.1 specifies that the minimum entry size is 33 bytes, because the value may be empty (name >= 1 byte + value == 0 + 32 bytes). For the default 4096-byte table this allocates only 120 slots (4096/34). Eviction in AddHeader is driven by byte usage (_max_size), not by slot count, so a peer can add 121 minimal 33-byte entries (121*33 = 3993 <= 4096) without triggering eviction. The 121st AddHeader then hits CHECK(!_header_queue.full()), which aborts the process.

Affected Scenarios:
Use a bRPC server that serves HTTP/2 or gRPC requests (e.g. via the h2 protocol) from an untrusted network. The malicious header block is processed during HPACK decoding of incoming requests without authentication.

How to Fix: 
(Choose one of the following options) 
1. Upgrade bRPC to version 1.18.0, which fixes this issue.
2. Apply this patch: https://github.com/apache/brpc/pull/3462

Note:
The fix sizes the dynamic table for the 33-byte minimum entry (max_size / (32 + 1)) and ensures at least one ring-buffer slot is kept when max_size is smaller than the minimum entry, so that initialization cannot fail on malloc(0).

## Affected

- `apache/brpc < 1.18.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.