Is CVE-2026-43972 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-43972 being exploited in the wild.

How severe is CVE-2026-43972?

Medium severity, with a CVSS score of 6.3, published 8 June 2026.

Which products and versions are affected?

Nine Nines Gun >= 2.0.0, < 2.4.0.

Is there a fix for CVE-2026-43972?

A patch was published on 2026-07-29: GitHub advisory updated with patch details Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-43972 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-43972?

Check whether you run Nine Nines Gun at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-43972: ninenines gun cross-origin cookie injection in gun_http2

Q: Is there a fix for CVE-2026-43972?

A patch was published on 2026-07-29: GitHub advisory updated with patch details Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-43972 attacked?

It is attacked over the network, in a software library.

Q: Am I affected by CVE-2026-43972?

Check whether you run Nine Nines Gun at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-43972 · Severity: medium · CVSS 6.3 · Published 2026-06-08

Gun is an HTTP client library for Erlang/Elixir applications. A vulnerability in its HTTP/2 implementation allows a malicious server to inject cookies for unrelated third-party websites into the client's cookie store. This could allow an attacker to hijack user accounts or perform session fixation attacks on other services the application interacts with.

Technologies: Nine Nines Gun. Vendors: Nine Nines.

Quick answers

Is CVE-2026-43972 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-43972 being exploited in the wild.
How severe is CVE-2026-43972?: Medium severity, with a CVSS score of 6.3, published 8 June 2026.
Which products and versions are affected?: Nine Nines Gun >= 2.0.0, < 2.4.0.
Is there a fix for CVE-2026-43972?: A patch was published on 2026-07-29: GitHub advisory updated with patch details Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-43972 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-43972?: Check whether you run Nine Nines Gun at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability exists in the gun_http2:push_promise_frame/7 function, where the :authority pseudo-header from an incoming PUSH_PROMISE frame is stored without verifying it matches the connection's origin. When gun_http2:headers_frame/9 subsequently processes response headers, it calls gun_cookies:set_cookie_header/7 using this unvalidated authority. This behavior violates RFC 9113 §8.4, which requires clients to reject pushes for resources the server is not authoritative for. An attacker-controlled HTTP/2 server can exploit this to plant cookies for arbitrary domains in the client's shared cookie store, facilitating session fixation or account takeover. The issue is fixed in version 2.4.0.

Affected products

ninenines gun >= 2.0.0, < 2.4.0

Identifiers

CVE-2026-43972
GHSA-36w4-95hv-5vwg

Timeline

2026-06-08: disclosed
2026-06-08: advisory
2026-07-29: patched: GitHub advisory updated with patch details

References

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