Apache bRPC: Integer Underflow in mcpack2pb Parser Leading to Denial of Service

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-74755
StatePUBLISHED
Assignerapache
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-21 12:17:22 UTC
Updated2026-10-26 21:10:00 UTC
DescriptionAn integer underflow in the mcpack2pb component of Apache bRPC (version < 1.18.0) on all platforms allows remote attackers to crash a bRPC server by sending a request containing a string field with a zero value_size. The UnparsedValue::as_string() function computes `_size - 1` without validating `_size`; when value_size is 0 the expression underflows to SIZE_MAX, resize() throws std::length_error, and because the exception is not caught on the request parsing path the process aborts (SIGABRT). Root Cause: In src/mcpack2pb/parser.cpp, UnparsedValue::as_string() resizes the output string to `_size - 1`, where `_size` is the value_size of a string field taken directly from the network data. A value_size of 0 underflows the unsigned size_t, and the subsequent resize() throws an exception that is not caught. Affected Scenarios: bRPC servers that accept nshead frames wired to the ubrpc mcpack2 adaptor (for example the NsheadService + UbrpcMcpack2Adaptor deployment pattern) can be crashed by a single unauthenticated request. Stock open-source bRPC registers the ubrpc/nshead_mcpack protocols as client-only, so default server configurations are not affected. How to Fix: 1. Upgrade bRPC to a version that includes this fix. 2. Apply the patch in PR  https://github.com/apache/brpc/pull/3450

Risk And Classification

EPSS: 0.002020000 probability, percentile 0.100180000 (date 2026-10-26)

Problem Types: CWE-191 | CWE-191 CWE-191 Integer Underflow (Wrap or Wraparound)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Apache Software Foundation Apache BRPC affected 1.18.0 semver Not specified

References

ReferenceSourceLinkTags
lists.apache.org/thread/2pf15ojj0vr7rtx95677kgtl1mx3gdgb [email protected] lists.apache.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Feng Zhijie (Independent security researcher) (en)

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