{"apiVersion":"1.0","identifier":"CVE-2026-72854","description":"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.","publishedAt":"2026-08-20T19:17:01","lastModifiedAt":"2026-08-20T19:17:01","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-72854","cvssScore":5.3,"cvssVector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:L","epssProbability":0.00113,"riskScore":0.54,"affectedProduct":"msgpack-c","affectedVersions":"unknown","vulnerabilityType":"Library","operatingSystems":[],"links":{"self":"https://www.redsauce.net/api/cves/CVE-2026-72854","webPages":{"es":"https://www.redsauce.net/es/cves/CVE-2026-72854","en":"https://www.redsauce.net/en/cves/CVE-2026-72854","fr":"https://www.redsauce.net/fr/cves/CVE-2026-72854","pt":"https://www.redsauce.net/pt/cves/CVE-2026-72854","de":"https://www.redsauce.net/de/cves/CVE-2026-72854","sk":"https://www.redsauce.net/sk/cves/CVE-2026-72854","el":"https://www.redsauce.net/el/cves/CVE-2026-72854"},"source":"https://nvd.nist.gov/vuln/detail/CVE-2026-72854"}}