# CVE-2026-74755: Apache bRPC integer underflow in mcpack2pb component

Source: https://junglewise.ai/threats/cve-2026-74755-an-integer-underflow-in-the-mcpack2pb-component-of-apache-brpc  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-21. Updated: 2026-10-21  
License: CC BY 4.0 with a link back

CVE-2026-74755 · Severity: info · Published 2026-10-21

Apache bRPC is an open-source RPC framework used for distributed systems communication. An integer underflow vulnerability in its mcpack2pb message parser allows remote attackers to crash bRPC servers that are configured to accept nshead frames with mcpack2 encoding. A single unauthenticated network request with a malformed message can cause the server process to abort, resulting in denial of service.

Technologies: [Apache Brpc](https://junglewise.ai/threats/technologies/brpc). Vendors: [Apache](https://junglewise.ai/threats/vendors/apache).

## Quick answers

**Is CVE-2026-74755 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-74755 being exploited in the wild.

**How severe is CVE-2026-74755?** Informational severity, published 21 October 2026.

**Which products and versions are affected?** Apache Brpc < 1.18.0.

**Is there a fix for CVE-2026-74755?** Yes: fixed in bRPC 1.18.0. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-74755 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-74755?** Check whether you run Apache Brpc at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in bRPC 1.18.0

## Technical details

The UnparsedValue::as_string() function in src/mcpack2pb/parser.cpp computes `_size - 1` without validating that _size is greater than zero. When a string field with value_size of 0 is received from the network, the unsigned size_t computation underflows to SIZE_MAX, causing std::string::resize() to throw std::length_error. This exception is not caught during request parsing, leading to process abort (SIGABRT). Attack vector is unauthenticated network access on servers running the NsheadService + UbrpcMcpack2Adaptor deployment pattern.

## Affected products

- Apache bRPC < 1.18.0

## Timeline

- 2026-10-21: disclosed

## References

- [https://github.com/](https://github.com/)
- [https://lists.apache.org/thread/2pf15ojj0vr7rtx95677kgtl1mx3gdgb](https://lists.apache.org/thread/2pf15ojj0vr7rtx95677kgtl1mx3gdgb)

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