# CVE-2026-56386: Apache bRPC: Integer Underflow and Out-of-Bounds Read in HTTP/2 DATA Frame Parser


- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 21 Oct 2026
- **Updated:** 21 Oct 2026
- **Also known as:** GHSA-wj5x-6jj2-m348

## What is CVE-2026-56386?

CVE-2026-56386 is a high-severity vulnerability in Apache bRPC, published on 21 Oct 2026. 

### Official description

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.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound)), CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-56386?


## How do I fix CVE-2026-56386?

No fix has been published for CVE-2026-56386 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-56386 being exploited?

There is no known exploitation of CVE-2026-56386 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-56386 and fix it if it is affected.

What it is: CVE-2026-56386 is a high-severity vulnerability in Apache bRPC, published on 21 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-56386 in the wild and no public exploit code.

Affected product: Apache bRPC. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-56386/ (Markdown: https://insights.sbomify.com/CVE-2026-56386/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-56386
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-56386
- OSV: https://osv.dev/vulnerability/CVE-2026-56386

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-56386/
Summaries are generated and may contain mistakes; the official description above is the record.