---
id: CVE-2026-56386
title: >-
  Apache bRPC: Integer Underflow and Out-of-Bounds Read in HTTP/2 DATA Frame
  Parser
summary: >-
  Integer underflow and out-of-bounds read in the HTTP/2 server DATA frame
  parser in Apache bRPC allows an unauthenticated remote attacker to cause
  denial of service by sending a malformed DATA frame with the PADDED flag set
  and a zero-len…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cvssSource: adp
cwe:
  - CWE-191
  - CWE-125
vendor: Apache Software Foundation
product: apache/brpc
affected:
  - apache/brpc < 1.18.0
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-10-21T13:07:50.344384Z'
published: '2026-10-21'
updated: '2026-10-21'
sourceUpdated: '2026-10-21T13:07:53.942Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-56386'
references:
  - url: 'https://lists.apache.org/thread/2pf15ojj0vr7rtx95677kgtl1mx3gdgb'
tags:
  - cve.org
ingestedAt: '2026-10-21T12:48:53.765Z'
---

## Overview

Integer underflow and out-of-bounds read in the HTTP/2 server DATA frame parser in Apache bRPC allows an unauthenticated remote attacker to cause denial of service by sending a malformed DATA frame with the PADDED flag set and a zero-length payload.

Root Cause:
The HTTP/2 DATA frame handler computed the fragment size from the attacker-controlled payload length and, when the PADDED flag was present, decremented the fragment size before ensuring that the frame contained the mandatory pad length byte. A zero-length padded DATA frame could therefore underflow the unsigned fragment size and read the pad length byte past the end of the frame buffer.

Affected Scenarios:
Apache bRPC servers that accept HTTP/2 traffic are affected when a remote client can send crafted HTTP/2 frames to the server. HTTP/2 may be reached through cleartext h2c detection on an HTTP port or through TLS ALPN negotiation.

How to Fix:
(Choose one of the following options)
1. Upgrade Apache bRPC to version 1.18.0, which fixes this issue.
2. Apply this patch:  https://github.com/apache/brpc/pull/3325 

Note:
The fix validates that a padded DATA frame has enough payload bytes for the pad length field before decrementing the fragment size or reading the pad length byte. Malformed zero-length padded DATA frames are rejected with HTTP/2 FRAME_SIZE_ERROR.

## Affected

- `apache/brpc < 1.18.0`

## Remediation

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