Vulnerability advisory
EEF-CVE-2026-43974
gun HTTP/1.1 client accepts unsolicited 101 Switching Protocols response allowing server-driven protocol hijack and OOM
Also known as CVE-2026-43974GHSA-2j82-37xg-f9wp
- CVSS 4.0
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
Affected versions
| Affected | Fixed in |
|---|---|
2.0.0 to before 2.4.0 | 2.4.0Advisories → |
Repository
| Affected commits | Fixed by commit |
|---|---|
| GIT github.com/ninenines/gun.git ↗ | |
| a3c2edbb8c807717e2f10520c6cf1e77a62eab2e to before 5b48068c29ce5e112cb149b5857c7d4dc319a81b | 5b48068c29ce5e112cb149b5857c7d4dc319a81b |
Also listed as affected (9)
| |
Description
Summary
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.