---
id: "CVE-2026-56386"
kind: "vulnerability"
aliases: ["CVE-2026-56386"]
title: "Apache bRPC: malformed HTTP/2 DATA frame crashes servers remotely"
severity: "high"
cvss: 7.5
epss: 0.00732
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["apache-brpc", "c++", "http2", "package", "rpc-servers"]
not_affected_if: ["no-http2-listener", "not-internet-reachable"]
published_at: "2026-10-21T12:17:21+00:00"
first_seen_at: "2026-10-23T21:57:28+00:00"
updated_at: "2026-10-25T03:16:55+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-56386", "first_seen_at": "2026-10-23T21:57:28+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-56386", "first_seen_at": "2026-10-24T13:15:54+00:00"}]
---

# Apache bRPC: malformed HTTP/2 DATA frame crashes servers remotely

A zero-length HTTP/2 DATA frame with the PADDED flag makes the bRPC HTTP/2 parser underflow a size counter and read past the buffer. An unauthenticated remote client can crash the server, a denial of service.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `grep -ri brpc` in the project's dependency lock files or build config to find the bRPC version in use
- Check whether the bRPC server listens on an HTTP port that accepts HTTP/2 (h2c or TLS ALPN)

## Fix

- Upgrade Apache bRPC to `1.18.0`
- Or apply the patch from https://github.com/apache/brpc/pull/3325

## Timeline

- 2026-10-23T21:57:28+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-56386
- 2026-10-24T13:15:54+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-56386

## From the sources

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_