{"id":"CVE-2026-43974","summary":"gun HTTP/1.1 client accepts unsolicited 101 Switching Protocols response allowing server-driven protocol hijack and OOM","details":"Unexpected Status Code or Return Value vulnerability in ninenines gun (gun_http module) allows a malicious HTTP server to force the client into raw protocol mode via an unsolicited 101 Switching Protocols response.\n\nIn gun_http:handle_inform/8, when a 101 Switching Protocols response is received over HTTP/1.1, the function verifies only that the Upgrade header is syntactically valid and that the stream reference is a plain reference(). It does not check whether the client ever sent an Upgrade or Connection: upgrade header on the corresponding request. Because this check is absent, any 101 response (solicited or not) causes gun to dispatch a gun_upgrade message to the caller and transition the entire connection to raw protocol mode.\n\nA malicious or compromised HTTP server can send an unsolicited 101 response to any HTTP/1.1 request, causing the gun client to abandon HTTP framing for that connection. Once in raw mode, gun_raw applies no flow control (flow=infinity) and re-arms socket active mode after every received packet, so the server can flood the client with arbitrary bytes. These are forwarded as unbounded gun_data messages to the owner process, exhausting its mailbox and BEAM memory, ultimately crashing the VM.\n\nThis issue affects gun: from 2.0.0 before 2.4.0.","aliases":["EEF-CVE-2026-43974"],"modified":"2026-07-08T08:09:35.961230306Z","published":"2026-06-08T14:12:36.957Z","database_specific":{"cna_assigner":"EEF","unresolved_ranges":[{"extracted_events":[{"introduced":"a3c2edbb8c807717e2f10520c6cf1e77a62eab2e"},{"fixed":"5b48068c29ce5e112cb149b5857c7d4dc319a81b"}],"source":"AFFECTED_FIELD"}],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43974.json","cwe_ids":["CWE-841"]},"references":[{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-43974"},{"type":"ADVISORY","url":"https://cna.erlef.org/cves/CVE-2026-43974.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43974.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-43974"},{"type":"FIX","url":"https://github.com/ninenines/gun/commit/5b48068c29ce5e112cb149b5857c7d4dc319a81b"},{"type":"PACKAGE","url":"https://github.com/ninenines/gun"},{"type":"PACKAGE","url":"https://github.com/ninenines/gun.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/ninenines/gun","events":[{"introduced":"33223e751267c5f249f3db1277c13904a1801b92"},{"fixed":"8cc70ed78fc946e5d9c49e92d84bde64ca12db1f"},{"fixed":"5b48068c29ce5e112cb149b5857c7d4dc319a81b"}],"database_specific":{"extracted_events":[{"introduced":"2.0.0"},{"fixed":"2.4.0"}],"source":["DESCRIPTION","REFERENCES"]}}],"versions":["2.3.0","2.2.0","2.1.0","2.0.1","2.0.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-43974.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"}]}