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.
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Exploitation outlook
- Low exploitation risk0.21% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 12% of all EPSS-scored CVEs.
Advisory coverage (1)
- mediumGHSA-36w4-95hv-5vwg: gun_http2 has an Origin Validation Error vulnerabilityghsa · 2026-06-08
External references
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