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🛡️ CVE-2026-43972 — gun

🟠 CVSS 7.2 — High ✅ No Known Exploit CWE-346 OSV
7.2
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

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

Summary

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.

Configuration

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

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. Rated impact: confidentiality none, integrity low, availability none.

CVSS metrics in full

The score comes from this vector: 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

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Attack requirements: Present — the target has to be in a particular state for the attack to work.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Confidentiality impact: None.
  • Integrity impact: Low — limited, and the attacker does not choose what is affected.
  • Availability impact: None.

Weakness class

CVE-2026-43972 is classified as CWE-346: Origin Validation Error. The origin of a message or request is not verified properly, so one source can pose as another.

Affected software

CVE-2026-43972 is recorded against 1 package.

  • gun

Timeline and source

Published on 8 June 2026 and last revised on 18 August 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from OSV.

References

cna.erlef.org (Web)
github.com (Fix)
hex.pm (Package)

Other advisories for this package

gun has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-346: Origin Validation Error) in other software:

Details

Severity HIGH
CVSS Score 7.2
CVSS Vector 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
CWE CWE-346
Public Exploit ✅ No
Source OSV
Published 2026-06-08
Updated 2026-08-20
Modified 2026-08-18

Affected Packages

Software From version Fixed in
gun — —

Similar Threats

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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

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