Weakness Type (CWE)

CWE-346 — CWE-346 Origin Validation Error

CAPEC

CVSS 4.0 Score

6.3

MEDIUM

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

Vulnerability description

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.

Affected

pkg:hex/gun

Module Source File Routine
gun_http2 src/gun_http2.erl gun_http2:push_promise_frame/7
gun_http2:headers_frame/9
Status Type Version Changes / Fixed in
affected semver ⓘ 2.0.0 < 2.4.0

pkg:github/ninenines/gun

Module Source File Routine
gun_http2 src/gun_http2.erl gun_http2:push_promise_frame/7
gun_http2:headers_frame/9
Status Type Version Changes / Fixed in
affected git ⓘ 871989eef5 < 567863ff53

Configurations

The vulnerability is exploitable only when gun is configured with a cookie_store and connects to an HTTP/2 server with server push enabled.

References

Credits

  • Finder: Peter Ullrich
  • Remediation developer: Loïc Hoguin

CVE record as JSON:  GET /cves/CVE-2026-43972.json
OSV record as JSON:  GET /osv/EEF-CVE-2026-43972.json