{"id":"CVE-2026-72854","title":"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","summary":"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 doubli…","severity":"medium","cvss":5.3,"cvssVector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:L","cwe":["CWE-190","CWE-787"],"vendor":"msgpack","product":"msgpack-c","affected":["msgpack-c <= 7.0.1"],"published":"2026-08-20","updated":"2026-09-24","sourceUpdated":"2026-09-24T20:06:30.133","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-72854","references":[{"url":"https://github.com/msgpack/msgpack-c","label":"disclosure@vulncheck.com"},{"url":"https://github.com/msgpack/msgpack-c/blob/c-7.0.1/example/lib_buffer_unpack.c","label":"disclosure@vulncheck.com"},{"url":"https://github.com/msgpack/msgpack-c/blob/c-7.0.1/include/msgpack/unpack.h#L219-L223","label":"disclosure@vulncheck.com"},{"url":"https://github.com/msgpack/msgpack-c/blob/c-7.0.1/src/unpack.c#L429-L502","label":"disclosure@vulncheck.com"},{"url":"https://github.com/msgpack/msgpack-c/issues/1181","label":"disclosure@vulncheck.com"},{"url":"https://www.vulncheck.com/advisories/msgpack-c-integer-overflow-in-msgpack-unpacker-expand-buffer-causes-a-false-success-undersized-reservation","label":"disclosure@vulncheck.com"},{"url":"https://github.com/msgpack/msgpack-c/issues/1181","label":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}],"tags":["nvd","cve.org","exploit-available"],"epss":0.00157,"epssPercentile":0.04077,"exploitAvailable":true,"ssvc":{"exploitation":"poc","automatable":"no","technicalImpact":"partial","timestamp":"2026-08-20T18:52:52.984726Z"},"ingestedAt":"2026-09-24T15:45:56.711Z","slug":"CVE-2026-72854","body":"## Overview\n\nmsgpack_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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":29.2,"likelihood":0,"exploitation":12,"ransomware":0},"changes":[]}