---
cve: "CVE-2026-43974"
severity: "HIGH"
cvss: 8.7
epss: "0.5%"
vendor: "ninenines"
kev: false
exploited: false
published: "2026-06-08 15:16:46"
tags: [cve, security, high]
source: tsecurity.de CVE-Dossier
exported: "2026-09-22T04:44:15+02:00"
---

# CVE-2026-43974

> 8.7 HIGH · 🧪 PoC

## Beschreibung

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-Vektor

```
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
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |

## Patch verfügbar (OSV)

- 8cc70ed78fc946e5d9c49e92d84bde64ca12db1f (Commit)
- 5b48068c29ce5e112cb149b5857c7d4dc319a81b (Commit)

## Referenzen

- <https://cna.erlef.org/cves/CVE-2026-43974.html>
- <https://osv.dev/vulnerability/EEF-CVE-2026-43974>
- <https://github.com/ninenines/gun/commit/5b48068c29ce5e112cb149b5857c7d4dc319a81b>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-43974) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_