---
cve: "CVE-2026-43972"
severity: "MEDIUM"
cvss: 6.3
epss: "0.2%"
vendor: "ninenines"
kev: false
exploited: false
published: "2026-06-08 14:12:38"
tags: [cve, security, medium]
source: tsecurity.de CVE-Dossier
exported: "2026-09-20T22:28:38+02:00"
---

# CVE-2026-43972

> 6.3 MEDIUM · 🧪 PoC

## Beschreibung

Origin Validation Error vulnerability in ninenines gun (gun_http2 module) allows cross-origin cookie injection via unvalidated HTTP/2 PUSH_PROMISE authority.

In gun_http2:push_promise_frame/7, the :authority pseudo-header from an incoming PUSH_PROMISE frame is stored verbatim into the promised stream record without checking that it matches the connection's origin. When gun_http2:headers_frame/9 later processes the response headers for the promised stream, it calls gun_cookies:set_cookie_header/7 with the unvalidated server-supplied authority before any status branching and before user code can act. This violates RFC 7540 §10.6 / RFC 9113 §8.4, which require receivers to treat as a protocol error any push for a resource the server is not authoritative for.

A malicious or compromised HTTP/2 server can plant cookies scoped to arbitrary third-party domains into the client's shared cookie store. This enables session fixation attacks against those domains and, if the planted cookie overrides a legitimate session token, may result in account takeover. No user interaction beyond making a normal HTTP/2 request to the attacker-controlled server is required.

This issue affects gun: from 2.0.0 before 2.4.0.

## CVSS-Vektor

```
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/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)
- 567863ff53802fed21c3b3f25812db7f7ae29676 (Commit)

## Referenzen

- <https://cna.erlef.org/cves/CVE-2026-43972.html>
- <https://osv.dev/vulnerability/EEF-CVE-2026-43972>
- <https://github.com/ninenines/gun/commit/567863ff53802fed21c3b3f25812db7f7ae29676>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-43972) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_