# CVE-2026-55736: Private action arguments can be set by user input in Ash

> Attackers can inject values into private action arguments in the Ash framework, potentially leading to privilege escalation or data integrity violations.

- **Severity:** Medium 5.9 (`CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Jun 2026
- **Updated:** 10 Jul 2026
- **Also known as:** EEF-CVE-2026-55736, GHSA-f4hc-ppw9-4hhw

## What is CVE-2026-55736?

CVE-2026-55736 is a medium-severity missing authorization vulnerability in ash-project ash, published on 23 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Improperly Controlled Modification of Dynamically-Determined Object Attributes vulnerability in ash-project ash allows a user to set the value of a private action argument that is intended to be controlled only by trusted server-side code.

Action arguments declared with public?: false are meant to be set internally (for example via Ash.Changeset.set_private_argument/3) and must not be settable from end-user input. When a changeset is built from a parameter map, Ash filters out private arguments, but the filtering is incomplete.

In the regular changeset path (for_create, for_update, for_destroy), private arguments are stripped only when the parameter key is an atom. When the key is a binary (string), as is the case for user-supplied parameters, the private argument is kept and the user controls its value. In the atomic path (Ash.Changeset.fully_atomic_changeset/4, also reached through atomic and bulk updates), private arguments are not stripped at all, regardless of whether the key is an atom or a binary.

An attacker who can submit parameters to an action that defines a private argument can therefore inject a value for that argument. Depending on how the application uses the argument (for example an acting_user_id driving authorization or record ownership), this can lead to an integrity violation or privilege escalation.

This issue affects ash: from 3.0.0 before 3.29.3.

Weakness: CWE-915 (Improperly Controlled Modification of Dynamically-Determined Object Attributes)

## Which versions are affected by CVE-2026-55736?

3 open source packages ship an affected version, including ash.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `ash` | Hex | From 3.0.0 | 3.29.3 |
| `ash` | Hex | From 3.0.0 | 3.29.3 |
| `ash` | Hex | From 3.0.0 | 3.29.3 |

## How do I fix CVE-2026-55736?

Upgrade ash to 3.29.3 or later.

## Is CVE-2026-55736 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55736 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55736 and fix it if it is affected.

What it is: CVE-2026-55736 is a medium-severity missing authorization vulnerability in ash-project ash, published on 23 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55736 exists.

Affected packages and fixed versions:
- ash (Hex): affected from 3.0.0; fixed in 3.29.3
- ash (Hex): affected from 3.0.0; fixed in 3.29.3
- ash (Hex): affected from 3.0.0; fixed in 3.29.3

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-55736/ (Markdown: https://insights.sbomify.com/CVE-2026-55736/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55736
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55736
- OSV: https://osv.dev/vulnerability/CVE-2026-55736

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55736/
Summaries are generated and may contain mistakes; the official description above is the record.