# CVE-2026-77856: Unbounded atom creation from typed struct field names in AshTypescript field selector

> An unauthenticated attacker can crash the Elixir node by exhausting the atom table via crafted field names in AshTypescript.

- **Severity:** High 8.2 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 Sep 2026
- **Updated:** 1 Sep 2026
- **Also known as:** EEF-CVE-2026-77856, GHSA-rj47-h936-4cxw

## What is CVE-2026-77856?

CVE-2026-77856 is a high-severity denial of service vulnerability in ash-project ash_typescript, published on 1 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Allocation of Resources Without Limits or Throttling vulnerability in ash-project ash_typescript allows an unauthenticated attacker to exhaust the BEAM atom table and abort the node via client-supplied typed struct field names.

resolve_typed_struct_field/2 in lib/ash_typescript/rpc/field_processing/field_selector.ex looks a client-supplied field name up in the typed struct's reverse map and, when it finds no match, falls back to String.to_atom/1. Because this runs before any field-existence check, an unresolvable name mints a permanent atom rather than being rejected as unknown. Atoms are never garbage collected, so a request carrying many distinct names on a typed struct field grows the atom table until the VM aborts at its limit.

This issue affects ash_typescript: from 0.11.0 before 0.18.0.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-77856?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `ash_typescript` | Hex | From 0.11.0 | 0.18.0 |

## How do I fix CVE-2026-77856?

Upgrade ash_typescript to 0.18.0 or later.

## Is CVE-2026-77856 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77856 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-77856 and fix it if it is affected.

What it is: CVE-2026-77856 is a high-severity denial of service vulnerability in ash-project ash_typescript, published on 1 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77856 exists.

Affected packages and fixed versions:
- ash_typescript (Hex): affected from 0.11.0; fixed in 0.18.0

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-2026-77856/ (Markdown: https://insights.sbomify.com/CVE-2026-77856/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77856
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77856
- OSV: https://osv.dev/vulnerability/CVE-2026-77856

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-77856/
Summaries are generated and may contain mistakes; the official description above is the record.