{"id":"CVE-2026-13343","summary":"Uninitialised stack memory disclosure in the MIDI 2.0 UMP Stream responder","details":"The UMP Stream responder library in lib/midi2/ump_stream_responder.c builds reply packets in a 16-byte struct midi_ump (uint32_t data[4]). The builders make_endpoint_info() and make_function_block_info() populate only the first two words (res.data[0] and res.data[1]) and, before this fix, declared their result as an uninitialised local (struct midi_ump res;). The remaining two words (res.data[2], res.data[3]) retain stale stack contents.\n\nEndpoint Info and Function Block Info notifications are UMP Stream messages (UMP_MT_UMP_STREAM), which are 4 words long, so the full 16-byte packet — including the two uninitialised words — is transmitted verbatim by cfg-\u003esend(). The responder is driven by attacker-supplied UMP Stream Endpoint-Discovery / Function-Block-Discovery requests via ump_stream_respond(). In the in-tree Network MIDI 2.0 server (subsys/net/lib/midi2/netmidi2.c) these requests arrive as UDP datagrams and, with the default no-authentication endpoint, a remote peer can establish a session and trigger the responses; the same library also serves USB MIDI 2.0 hosts.\n\nEach discovery request causes the device to disclose 8 bytes of its own uninitialised stack memory to the peer, and the request is freely repeatable. This is a confidentiality-only information leak (root cause is use of an uninitialised variable, CWE-457/CWE-908); the leaked words could include residual data or pointer values. There is no memory-corruption, integrity, or availability impact.\n\nThe fix zero-initialises both result structs (struct midi_ump res = {0};), so the trailing words are cleared before transmission. These are the only two responder builders that left trailing words unset (send_string() already zeroes its buffer), so the leak is fully closed.","aliases":["GHSA-4w5x-w7j4-6xxc"],"modified":"2026-08-28T14:32:56.189922Z","published":"2026-08-24T15:43:36.665Z","database_specific":{"cna_assigner":"zephyr","cwe_ids":["CWE-200"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/13xxx/CVE-2026-13343.json"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/13xxx/CVE-2026-13343.json"},{"type":"ADVISORY","url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-4w5x-w7j4-6xxc"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-13343"},{"type":"FIX","url":"https://github.com/zephyrproject-rtos/zephyr/commit/255e64bd22fcd02bd437bb0d6badac87c67de23b"},{"type":"PACKAGE","url":"https://github.com/zephyrproject-rtos/zephyr"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/zephyrproject-rtos/zephyr","events":[{"introduced":"3568e1b6d5cdd51a6b964a2a1d6d29200fea2056"},{"fixed":"255e64bd22fcd02bd437bb0d6badac87c67de23b"}],"database_specific":{"source":["AFFECTED_FIELD","REFERENCES"],"extracted_events":[{"introduced":"4.3.0"},{"fixed":"4.4.2"}]}}],"versions":["v4.4.0","v4.4.0-rc3","v4.4.0-rc2","v4.4.0-rc1","v4.3.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-13343.json","vanir_signatures_modified":"2026-08-28T14:32:56Z","vanir_signatures":[{"deprecated":false,"digest":{"length":620,"function_hash":"319473042137286261314935565378441264561"},"id":"CVE-2026-13343-7fc09805","signature_type":"Function","signature_version":"v1","source":"https://github.com/zephyrproject-rtos/zephyr/commit/255e64bd22fcd02bd437bb0d6badac87c67de23b","target":{"file":"lib/midi2/ump_stream_responder.c","function":"make_function_block_info"}},{"deprecated":false,"digest":{"function_hash":"331005920418431437594468625656475816397","length":324},"id":"CVE-2026-13343-891dedb2","signature_type":"Function","signature_version":"v1","source":"https://github.com/zephyrproject-rtos/zephyr/commit/255e64bd22fcd02bd437bb0d6badac87c67de23b","target":{"file":"lib/midi2/ump_stream_responder.c","function":"make_endpoint_info"}},{"signature_version":"v1","source":"https://github.com/zephyrproject-rtos/zephyr/commit/255e64bd22fcd02bd437bb0d6badac87c67de23b","target":{"file":"lib/midi2/ump_stream_responder.c"},"deprecated":false,"digest":{"line_hashes":["171322162529502558433863689741312351131","173541473214353049875235015427037062103","323459552637991437510046112581699683377","219154023740064300794351881061103389056","295404652830550670293043892550563318658","266086277789136195707918016971229408443","312826903352315478559532990303605132044","85222813731231729653405347957623660477"],"threshold":0.9},"id":"CVE-2026-13343-c0a16f6b","signature_type":"Line"}]}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N"}]}