{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-43974", "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "state": "PUBLISHED", "assignerShortName": "EEF", "dateReserved": "2026-05-04T18:23:25.574Z", "datePublished": "2026-06-08T14:12:36.957Z", "dateUpdated": "2026-06-08T16:34:38.989Z"}, "containers": {"cna": {"affected": [{"cpes": ["cpe:2.3:a:ninenines:gun:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["gun_http"], "packageName": "gun", "packageURL": "pkg:hex/gun", "product": "gun", "programFiles": ["src/gun_http.erl"], "programRoutines": [{"name": "gun_http:handle_inform/8"}], "repo": "https://github.com/ninenines/gun", "vendor": "ninenines", "versions": [{"lessThan": "2.4.0", "status": "affected", "version": "2.0.0", "versionType": "semver"}]}, {"collectionURL": "https://github.com", "cpes": ["cpe:2.3:a:ninenines:gun:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["gun_http"], "packageName": "ninenines/gun", "packageURL": "pkg:github/ninenines/gun", "product": "gun", "programFiles": ["src/gun_http.erl"], "programRoutines": [{"name": "gun_http:handle_inform/8"}], "repo": "https://github.com/ninenines/gun.git", "vendor": "ninenines", "versions": [{"lessThan": "5b48068c29ce5e112cb149b5857c7d4dc319a81b", "status": "affected", "version": "a3c2edbb8c807717e2f10520c6cf1e77a62eab2e", "versionType": "git"}]}], "cpeApplicability": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:ninenines:gun:*:*:*:*:*:*:*:*", "versionEndExcluding": "2.4.0", "versionStartIncluding": "2.0.0", "vulnerable": true}], "negate": false, "operator": "OR"}], "operator": "AND"}], "credits": [{"lang": "en", "type": "finder", "value": "Peter Ullrich"}, {"lang": "en", "type": "remediation developer", "value": "Lo\u00efc Hoguin"}], "descriptions": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "Unexpected Status Code or Return Value vulnerability in ninenines gun (<tt>gun_http</tt> module) allows a malicious HTTP server to force the client into raw protocol mode via an unsolicited 101 Switching Protocols response.<p>In <tt>gun_http:handle_inform/8</tt>, when a <tt>101 Switching Protocols</tt> response is received over HTTP/1.1, the function verifies only that the <tt>Upgrade</tt> header is syntactically valid and that the stream reference is a plain <tt>reference()</tt>. It does not check whether the client ever sent an <tt>Upgrade</tt> or <tt>Connection: upgrade</tt> header on the corresponding request. Because this check is absent, any 101 response (solicited or not) causes gun to dispatch a <tt>gun_upgrade</tt> message to the caller and transition the entire connection to raw protocol mode.</p><p>A 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, <tt>gun_raw</tt> applies no flow control (<tt>flow=infinity</tt>) and re-arms socket <tt>active</tt> mode after every received packet, so the server can flood the client with arbitrary bytes. These are forwarded as unbounded <tt>gun_data</tt> messages to the owner process, exhausting its mailbox and BEAM memory, ultimately crashing the VM.</p><p>This issue affects gun: from 2.0.0 before 2.4.0.</p>"}], "value": "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. 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Because this check is absent, any 101 response (solicited or not) causes gun to dispatch a <tt>gun_upgrade</tt> message to the caller and transition the entire connection to raw protocol mode.</p><p>A 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, <tt>gun_raw</tt> applies no flow control (<tt>flow=infinity</tt>) and re-arms socket <tt>active</tt> mode after every received packet, so the server can flood the client with arbitrary bytes. 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