Weakness Type (CWE)

CWE-841 — CWE-841 Improper Enforcement of Behavioral Workflow

CAPEC

CVSS 4.0 Score

8.7

HIGH

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

Vulnerability description

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.

Affected

pkg:hex/gun

Module Source File Routine
gun_http src/gun_http.erl gun_http:handle_inform/8
Status Type Version Changes / Fixed in
affected semver ⓘ 2.0.0 < 2.4.0

pkg:github/ninenines/gun

Module Source File Routine
gun_http src/gun_http.erl gun_http:handle_inform/8
Status Type Version Changes / Fixed in
affected git ⓘ a3c2edbb8c < 5b48068c29

References

Credits

  • Finder: Peter Ullrich
  • Remediation developer: Loïc Hoguin

CVE record as JSON:  GET /cves/CVE-2026-43974.json
OSV record as JSON:  GET /osv/EEF-CVE-2026-43974.json