{"id":"DEBIAN-CVE-2026-72854","details":"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.","modified":"2026-09-25T08:47:26.716078861Z","published":"2026-08-20T19:17:01.040Z","upstream":["CVE-2026-72854"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-72854"}],"affected":[{"package":{"name":"msgpack-c","ecosystem":"Debian:12","purl":"pkg:deb/debian/msgpack-c?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["4.0.0-3","6.0.0-1","6.0.0-2","6.0.0-3","6.0.0-4","6.0.0-5","6.0.1-1","6.0.1-2","6.0.1-3","6.1.0-1","6.1.0-2","7.0.1-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-72854.json"}},{"package":{"name":"msgpack-c","ecosystem":"Debian:13","purl":"pkg:deb/debian/msgpack-c?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.0.1-3","6.1.0-1","6.1.0-2","7.0.1-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-72854.json"}},{"package":{"name":"msgpack-c","ecosystem":"Debian:14","purl":"pkg:deb/debian/msgpack-c?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.0.1-3","6.1.0-1","6.1.0-2","7.0.1-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-72854.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:L"}]}