# CVE-2026-74757: Apache bRPC: Uncontrolled Memory Allocation via Malicious mcpack Array Item Count


- **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:** 26 Oct 2026
- **Also known as:** GHSA-px5f-q4rm-r7jp

## What is CVE-2026-74757?

CVE-2026-74757 is a high-severity vulnerability in Apache bRPC, published on 21 Oct 2026. 

### Official description

Uncontrolled resource allocation in the mcpack2pb component in Apache bRPC (version < 1.18.0) on all platforms allows remote attackers to make the server allocate a large amount of memory via sending a crafted mcpack request with a huge array item count.

Root Cause:
The bRPC mcpack2pb parser trusts the item count stored in the mcpack array header without validating it against the actual payload size. The code generated by the mcpack2pb protoc plugin uses this count to preallocate memory for repeated protobuf fields via Reserve(). A malformed request declaring item_count = 0x7fffffff can force the server to preallocate about 16GB of virtual memory, which may abort the process (SIGABRT) on memory-constrained hosts.

Affected Scenarios:
Use a bRPC server that wires a NsheadService to UbrpcMcpack2Adaptor (the Baidu ubrpc deployment pattern) and parses requests with code generated by the mcpack2pb protoc plugin. The request body is parsed before 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/3451 

Note:
No matter which option you choose, you should know that the fix caps the array item count to the remaining bytes of the array payload.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-74757?


## How do I fix CVE-2026-74757?

No fix has been published for CVE-2026-74757 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-74757 being exploited?

There is no known exploitation of CVE-2026-74757 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74757 and fix it if it is affected.

What it is: CVE-2026-74757 is a high-severity vulnerability in Apache bRPC, published on 21 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-74757 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-2026-74757/ (Markdown: https://insights.sbomify.com/CVE-2026-74757/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74757
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74757
- OSV: https://osv.dev/vulnerability/CVE-2026-74757

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-74757/
Summaries are generated and may contain mistakes; the official description above is the record.