How severe is CVE-2026-43972?

No CVSS score has been assigned to CVE-2026-43972 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-43972?

CVE-2026-43972 affects the following packages: gun (Hex). Ecosystems affected: Hex.

How do I fix CVE-2026-43972?

Update gun to 2.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-43972 is resolved across your whole dependency graph.

How do I detect CVE-2026-43972 in my Hex dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for gun, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-43972 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-43972?

O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-43972 can be triaged on real exposure rather than presence alone.

Is CVE-2026-43972 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-43972 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-43972?

CVE-2026-43972 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 7th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-43972?

CVE-2026-43972 is classified as CWE-346 (CWE-346). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-43972 published, and has it been updated?

CVE-2026-43972 was published on June 8, 2026 and was last updated on August 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💧 Hex

Not in CISA KEV

CVE-2026-43972 — gun

Fix: ninenines/gun@567863f

CVE-2026-43972 is a CWE-346 vulnerability in gun. A fix is available for gun — see the affected versions and patch details below.

gun HTTP/2 PUSH_PROMISE authority not validated against connection origin allows cross-origin cookie injection

Also known asEEF-CVE-2026-43972GHSA-36w4-95hv-5vwg

Published

Jun 8, 2026

Updated

Aug 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Sep 19, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-43972.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs7th percentile — riskier than 7% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Real-World Exposure

1 pkg affected

💧gun

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Hex packages — download data is not available via public APIs for these ecosystems.

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 Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
💧Hex	`gun`	≥ 2.0.0&&< 2.4.0	2.4.0`mix deps.update gun`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for gun, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update gun to 2.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-43972 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-43972 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2026-43972. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

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 ca

O3 Security · Impact-Aware SCA

Is CVE-2026-43972 in your dependencies?

O3 Security finds CVE-2026-43972 across Hex dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

Scan my dependencies How O3 SCA works