CVE-2026-43974

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. In 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. 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, 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. This issue affects gun: from 2.0.0 before 2.4.0.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://cna.erlef.org/cves/CVE-2026-43974.html	Third Party Advisory
https://github.com/ninenines/gun/commit/5b48068c29ce5e112cb149b5857c7d4dc319a81b	Patch
https://osv.dev/vulnerability/EEF-CVE-2026-43974	Third Party Advisory Patch

Configurations

Configuration 1 (hide)

cpe:2.3:a:ninenines:gun:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-06-08 15:16

Updated : 2026-08-18 15:44

NVD link : CVE-2026-43974

Mitre link : CVE-2026-43974

CVE.ORG link : CVE-2026-43974

JSON object : View

Products Affected

ninenines

gun

CWE

CWE-841

Improper Enforcement of Behavioral Workflow

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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."}, {"lang": "es", "value": "Una vulnerabilidad de c\u00f3digo de estado o valor de retorno inesperado en ninenines gun (m\u00f3dulo gun_http) permite a un servidor HTTP malicioso forzar al cliente a un modo de protocolo sin procesar a trav\u00e9s de una respuesta 101 Switching Protocols no solicitada.\n\nEn gun_http:handle_inform/8, cuando se recibe una respuesta 101 Switching Protocols sobre HTTP/1.1, la funci\u00f3n verifica solo que el encabezado Upgrade es sint\u00e1cticamente v\u00e1lido y que la referencia de flujo es una referencia simple(). No verifica si el cliente alguna vez envi\u00f3 un encabezado Upgrade o Connection: upgrade en la solicitud correspondiente. Debido a que esta verificaci\u00f3n est\u00e1 ausente, cualquier respuesta 101 (solicitada o no) hace que gun env\u00ede un mensaje gun_upgrade al llamador y transicione toda la conexi\u00f3n a modo de protocolo sin procesar.\n\nUn servidor HTTP malicioso o comprometido puede enviar una respuesta 101 no solicitada a cualquier solicitud HTTP/1.1, haciendo que el cliente gun abandone el encuadre HTTP para esa conexi\u00f3n. Una vez en modo sin procesar, gun_raw no aplica control de flujo (flow=infinity) y rearma el modo activo del socket despu\u00e9s de cada paquete recibido, por lo que el servidor puede inundar al cliente con bytes arbitrarios. Estos se reenv\u00edan como mensajes gun_data ilimitados al proceso propietario, agotando su buz\u00f3n y la memoria BEAM, lo que finalmente provoca el bloqueo de la VM.\n\nEste problema afecta a gun: desde 2.0.0 antes de 2.4.0."}], "lastModified": "2026-08-18T15:44:36.187", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:ninenines:gun:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "749B0FB5-7AC7-4FAB-A461-90450AA8AC67", "versionEndExcluding": "2.4.0", "versionStartIncluding": "2.0.0"}], "operator": "OR"}]}], "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}