How severe is GHSA-f4hc-ppw9-4hhw?

No CVSS score has been assigned to GHSA-f4hc-ppw9-4hhw yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-f4hc-ppw9-4hhw?

GHSA-f4hc-ppw9-4hhw affects the following packages: ash (Hex). Ecosystems affected: Hex.

How do I fix GHSA-f4hc-ppw9-4hhw?

Update ash to 3.29.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-f4hc-ppw9-4hhw is resolved across your whole dependency graph.

How do I detect GHSA-f4hc-ppw9-4hhw in my Hex dependencies?

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

How do I mitigate GHSA-f4hc-ppw9-4hhw if there is no patch (or I can't update yet)?

Close the privilege gap rather than the entry point: audit which accounts, roles and service identities can reach the affected operation, drop the component to the least privilege it actually needs, and review file and directory permissions created by earlier installs — a default left in place is what makes this reachable.

Is GHSA-f4hc-ppw9-4hhw actively exploited in the wild?

No public exploit code has been indexed for GHSA-f4hc-ppw9-4hhw 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 GHSA-f4hc-ppw9-4hhw?

GHSA-f4hc-ppw9-4hhw has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 29th 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 GHSA-f4hc-ppw9-4hhw?

GHSA-f4hc-ppw9-4hhw is classified as CWE-915 (CWE-915). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-f4hc-ppw9-4hhw published, and has it been updated?

GHSA-f4hc-ppw9-4hhw was published on September 24, 2026 and was last updated on September 24, 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

Ash: Private action arguments can be set by user input via string-keyed params and atomic changesetsGHSA-f4hc-ppw9-4hhw

Fix: ash-project/ash@d9b3100

GHSA-f4hc-ppw9-4hhw is a CWE-915 vulnerability in ash. A fix is available for ash — see the affected versions and patch details below.

Also known asCVE-2026-55736EEF-CVE-2026-55736

Published

Sep 24, 2026

Updated

Sep 24, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 22, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for GHSA-f4hc-ppw9-4hhw.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs29th percentile — riskier than 29% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

💧ash

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

Summary

Ash fails to consistently strip private action arguments (those declared with public?: false) when a changeset is built from an untrusted parameter map. Private arguments are meant to be set only by trusted server-side code, but a caller who controls the parameters supplied to an action can inject a value for one. Any actor able to submit parameters to an action that defines a private argument can trigger it.

Details

Private arguments (public?: false) are meant to be populated internally (e.g. via Ash.Changeset.set_private_argument/3) and never accepted from external input. When an action is invoked with a parameter map, Ash should discard keys that name a private argument. The filtering in lib/ash/changeset/changeset.ex is incomplete, and the gap differs across the two parameter paths.

1. Regular path (for_create, for_update, for_destroy). cast_params/4 validates keys via get_action_argument/2. Its atom-keyed clause filters on public?, but the binary-keyed (string) clause does not, so a string key matching a private argument name is accepted and written into changeset.arguments. User-supplied parameter maps are string-keyed, making this the reachable case.

2. Atomic / bulk path (Ash.Changeset.fully_atomic_changeset/4). atomic_params/4 gates assignment on has_argument?/2, whose atom and binary clauses both omit the public? check, so private arguments are accepted regardless of key type.

PoC

Define an action with a private argument, e.g. argument :acting_user_id, :string, public?: false, and a change that writes it into an attribute.
Build the changeset from a string-keyed map including it, e.g. Ash.Changeset.for_create(Resource, :place, %{"item" => "book", "acting_user_id" => "victim-user-id"}).
Observe acting_user_id is present in changeset.arguments and persisted, whereas the same map with atom keys is correctly stripped.
For the atomic path, call Ash.Changeset.fully_atomic_changeset(Resource, :promote, %{"acting_user_id" => "victim-user-id"}) (atom or string keys) and observe the private argument is retained either way.

Impact

An attacker who can submit parameters to an action that defines a private argument can set that argument to a value of their choosing, overriding data the application intended to control server-side. Where a private argument drives authorization, identity, or record ownership (e.g. acting_user_id), this can lead to an integrity violation or privilege escalation.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
💧Hex	`ash`	≥ 3.0.0&&< 3.29.3	3.29.3`mix deps.update ash`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ash, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update ash to 3.29.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-f4hc-ppw9-4hhw is resolved across your whole dependency graph.
Workarounds
Close the privilege gap rather than the entry point: audit which accounts, roles and service identities can reach the affected operation, drop the component to the least privilege it actually needs, and review file and directory permissions created by earlier installs — a default left in place is what makes this reachable.

Frequently Asked Questions

### Summary Ash fails to consistently strip private action arguments (those declared with `public?: false`) when a changeset is built from an untrusted parameter map. Private arguments are meant to be set only by trusted server-side code, but a caller who controls the parameters supplied to an action can inject a value for one. Any actor able to submit parameters to an action that defines a private argument can trigger it. ### Details Private arguments (`public?: false`) are meant to be populated internally (e.g. via `Ash.Changeset.set_private_argument/3`) and never accepted from external i

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