EEF-CVE-2026-53426
Atom-table exhaustion denial-of-service via JSON parse_document in MDEx
Details
## Summary
Allocation of Resources Without Limits or Throttling vulnerability in leandrocp MDEx allows Excessive Allocation.
MDEx.parse\_document/2 accepts a {:json, json} source. In lib/mdex.ex, the private json\_to\_node/1 function passes the attacker-controlled node\_type value to Module.concat/1, which calls String.to\_atom/1 and interns a brand-new atom for every distinct value. Atoms are never garbage collected on the BEAM, so a crafted JSON document carrying a unique node\_type at each (deeply nested) node mints one permanent atom per node.
A single document can intern hundreds of thousands of atoms, and a large enough document exhausts the default atom table (around 1,048,576 atoms) and aborts the entire Erlang VM, taking down every process on the node. Any application that passes untrusted input to the {:json, ...} source of MDEx.parse\_document is exposed to an unauthenticated denial-of-service.
This issue affects mdex from 0.4.3 before 0.13.2.
## Workaround
Do not pass untrusted or attacker-controlled input to the {:json, ...} source of MDEx.parse\_document/2. The {:markdown, ...} source is not affected.
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