An 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
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
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Apache Software Foundation | Apache bRPC | unaffected |
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Wed, 21 Oct 2026 12:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | An 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 | |
| Title | Apache bRPC: Integer Underflow in mcpack2pb Parser Leading to Denial of Service | |
| Weaknesses | CWE-191 | |
| References |
|
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MITRE
Status: PUBLISHED
Assigner: apache
Published:
Updated: 2026-10-21T11:45:25.658Z
Reserved: 2026-08-15T06:31:05.828Z
Link: CVE-2026-74755
Vulnrichment
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NVD
Status : Received
Published: 2026-10-21T12:17:22.550
Modified: 2026-10-21T12:17:22.550
Link: CVE-2026-74755
Redhat
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Weaknesses