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CVE-2026-77856 – Unauthenticated Denial of Service via Atom Table Exhaustion – ash_typescript 0.11.0

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Summary

CVE-2026-77856 is a denial-of-service vulnerability in ash_typescript, an Elixir/Ash Framework library that generates TypeScript RPC clients. Unauthenticated attackers can crash an entire BEAM node by submitting crafted field-name requests that are converted into permanent, unbounded Erlang atoms before validation, eventually exhausting the VM’s atom table. The issue has a CVSS base score of 8.2 (High) and requires no authentication or user interaction to exploit.

Technical details

  • Root cause: The resolve_typed_struct_field/2 function in lib/ash_typescript/rpc/field_processing/field_selector.ex calls String.to_atom/1 to look up client-supplied field names on resources backed by Ash.TypedStruct, and does so before verifying that the field actually exists on the struct.
  • Why it’s exploitable: In the BEAM VM, atoms are never garbage-collected. Any distinct string converted via String.to_atom/1 permanently consumes atom table space (default limit ~1,048,576 atoms). By repeatedly sending unique, invalid field names, an attacker can drive the atom table to its limit.
  • Trigger conditions: The target application must expose at least one Ash RPC action operating on a resource that includes a field backed by Ash.TypedStruct.
  • Attack vector: Network-based (AV:N), low attack complexity, requires privileges (PR:N) — no authentication needed, and no user interaction is required.
  • Impact: Once the atom table is exhausted, the entire BEAM node crashes, causing a complete denial of service for every application running on that node (not just ash_typescript). Recovery requires a manual node restart.
  • Note: this issue was not fully addressed by an earlier, similar fix that targeted atom creation in field formatters; the typed-struct field resolution path was a separate, unpatched code path.

Affected software

  • ash_typescript versions 0.11.0 through 0.17.x (all versions prior to 0.18.0)

Severity

  • CVSS Score: 8.2 (High)
  • Vector (CVSS v4.0): 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
    (Note: the vendor advisory and CVE record publish this score using the CVSS v4.0 standard rather than v3.1.)

Mitigation and recommended actions

  • Immediate: Upgrade ash_typescript to version 0.18.0 or later, which validates field existence before any atom conversion occurs.
  • If immediate patching is not possible:
    • Restrict or disable public exposure of RPC actions on Ash resources containing Ash.TypedStruct-backed fields until the upgrade can be applied.
    • Monitor BEAM VM atom table usage (e.g., via :erlang.system_info(:atom_count)) and alert on abnormal growth as an early warning sign of exploitation attempts.
    • Apply rate limiting or WAF rules to RPC endpoints to reduce the volume of distinct field-name payloads an attacker can submit.

References

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