Vulnerability in Ninenines Gun
CVE-2026-43972
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.002 (9.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 9th percentile — 9.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000
Affected products
Weakness classification (CWE)
References
- 6b3ad84c-e1a6-4bf7-a703-f496b71e49db (related, Patch, Third Party Advisory, third-party-advisory)
- 6b3ad84c-e1a6-4bf7-a703-f496b71e49db (Patch, patch)
- 6b3ad84c-e1a6-4bf7-a703-f496b71e49db (related, Third Party Advisory)
Frequently asked questions
- What is CVE-2026-43972?
- CVE-2026-43972 is a high-severity vulnerability in Ninenines Gun, classified under Origin Validation Error. CVSS score: 7.2/10. Published 2026-06-08.
- How severe is CVE-2026-43972?
- High severity. CVSS v3 base score is 7.2 out of 10.