Integer Overflow or Wraparound Affecting msgpack-c package, versions *


Severity

Recommended
0.0
medium
0
10

Snyk's Security Team recommends NVD's CVSS assessment. Learn more

Threat Intelligence

EPSS
0.16% (5th percentile)

Do your applications use this vulnerable package?

In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.

Test your applications
  • Snyk IDSNYK-ECHOLATEST-MSGPACKC-19165826
  • published22 Aug 2026
  • disclosed20 Aug 2026

Introduced: 20 Aug 2026

CVE-2026-72854  (opens in a new tab)
CWE-190  (opens in a new tab)
CWE-787  (opens in a new tab)

How to fix?

There is no fixed version for Echo:latest msgpack-c.

NVD Description

Note: Versions mentioned in the description apply only to the upstream msgpack-c package and not the msgpack-c package as distributed by Echo. See How to fix? for Echo:latest relevant fixed versions and status.

msgpack_unpacker_expand_buffer in src/unpack.c, reached through the public msgpack_unpacker_reserve_buffer API, computes its new buffer size using an unchecked size_t addition of the requested size and the amount already used. The doubling loop guards its own multiplication against overflow, but the addition in the loop condition is unguarded, so a request near SIZE_MAX wraps: the loop condition is already satisfied, the allocation is performed at the small pre-wrap size, and the function returns true. The caller is told the requested capacity was reserved when it was not, so a subsequent write of the requested length overflows the heap buffer. The library's own example/lib_buffer_unpack.c demonstrates the reserve-then-write pattern, and its defensive assert comparing capacity against the request is compiled out under NDEBUG. msgpack-c's own decode entry points do not derive the reservation size from untrusted input, so reaching this requires an integration that passes an attacker-influenced length to the reservation API, such as a length-prefixed streaming transport.

CVSS Base Scores

version 3.1