# CVE-2026-86338: Ash field policies do not filter-nil forbidden calculations and aggregates, enabling an information-disclosure oracle

> Attackers can bypass field policies to read protected calculation and aggregate values via filter-based oracles in the Ash framework.

- **Severity:** Medium 6.0 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Sep 2026
- **Updated:** 16 Sep 2026
- **Also known as:** EEF-CVE-2026-86338, GHSA-7qr8-wrvq-566q, GHSA-h9mg-hh48-hrwv

## What is CVE-2026-86338?

CVE-2026-86338 is a medium-severity vulnerability in ash-project ash, published on 16 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Ash field_policies are documented to protect against filter-based information disclosure: when a field the actor may not see is referenced in a filter, it is replaced with an expression that evaluates to nil, so a filter cannot be used as a yes/no oracle to read a value the actor cannot see.

This nilling was applied to attributes but not to calculations or aggregates. A user-supplied filter reference to a calculation or aggregate carries an Ash.Query.Calculation / Ash.Query.Aggregate struct, which the authorizer's reference replacement did not match (it only matched the Ash.Resource.* structs), so the filter ran against the real value.

As a result, an actor whose field policies forbid a calculation or aggregate can still filter by it (for example filter(secret_calc == "x") or filter(comment_count == n)) and learn the value from whether rows match — an oracle that recovers field-policy-protected values one probe at a time. Filtering is commonly exposed to lower-privileged actors (for example via AshGraphql or AshJsonApi filter arguments), which is exactly the surface field policies are meant to protect.

The fix routes filter references to calculations and aggregates through the same field-policy nilling as attributes.

This issue affects ash: from 2.11.0-rc.0 before 3.33.4.

Weakness: CWE-1220 (Insufficient Granularity of Access Control)

## Which versions are affected by CVE-2026-86338?

1 open source package ship an affected version, including ash.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `ash` | Hex | From 2.11.0-rc.0 | 3.33.4 |

## How do I fix CVE-2026-86338?

Upgrade ash to 3.33.4 or later.

## Is CVE-2026-86338 being exploited?

There is no known exploitation of CVE-2026-86338 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-86338 and fix it if it is affected.

What it is: CVE-2026-86338 is a medium-severity vulnerability in ash-project ash, published on 16 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-86338 in the wild and no public exploit code.

Affected packages and fixed versions:
- ash (Hex): affected from 2.11.0-rc.0; fixed in 3.33.4

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-2026-86338/ (Markdown: https://insights.sbomify.com/CVE-2026-86338/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-86338
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-86338
- OSV: https://osv.dev/vulnerability/CVE-2026-86338

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-86338/
Summaries are generated and may contain mistakes; the official description above is the record.