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"cveId": "CVE-2026-74755",
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"state": "PUBLISHED",
"assignerShortName": "apache",
"dateReserved": "2026-08-15T06:31:05.828Z",
"datePublished": "2026-10-21T11:45:25.658Z",
"dateUpdated": "2026-10-30T17:56:42.592Z"
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"title": "Apache bRPC: Integer Underflow in mcpack2pb Parser Leading to Denial of Service",
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"descriptions": [
{
"description": "CWE-191 Integer Underflow (Wrap or Wraparound)",
"lang": "en",
"cweId": "CWE-191",
"type": "CWE"
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"vendor": "Apache Software Foundation",
"product": "Apache bRPC",
"packageURL": "pkg:github/apache/brpc",
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"version": "0",
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"value": "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).\n\nRoot Cause:\nIn 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.\n\nAffected Scenarios:\nbRPC 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.\n\nHow to Fix:\n1. Upgrade bRPC to a version that includes this fix.\n2. Apply the patch in PR https://github.com/apache/brpc/pull/3450",
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"value": "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 "
}
]
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"references": [
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"url": "https://lists.apache.org/thread/2pf15ojj0vr7rtx95677kgtl1mx3gdgb",
"tags": [
"vendor-advisory"
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"value": "GENERAL"
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"credits": [
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"value": "Feng Zhijie (Independent security researcher)",
"type": "finder"
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"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"integrityImpact": "NONE",
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"attackComplexity": "LOW",
"availabilityImpact": "HIGH",
"privilegesRequired": "NONE",
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"content": {
"timestamp": "2026-10-30T17:56:37.339174Z",
"id": "CVE-2026-74755",
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