CVE-2026-53426
HighCVSS 8.2Exploitation Probability (EPSS)
Low risk3th percentile - higher than 3% of all known CVEs
Summary
A vulnerability in the MDEx library for Elixir/Erlang allows exhaustion of the atom table by processing a specially crafted JSON document. The json_to_node/1 function creates new atoms for each unique node_type value, which are never garbage collected, leading to a crash of the entire BEAM virtual machine.
Risk Assessment
An unauthenticated attacker can send a malicious JSON document causing a denial-of-service (DoS) of the entire Erlang node, stopping all processes running on it. This affects any application that passes untrusted input to MDEx.parse_document/2 with a {:json, json} source.
Recommendation
Immediately update the mdex library to version 0.13.2 or later. If an update is not possible, restrict access to the MDEx.parse_document/2 function for untrusted data or implement validation of JSON document size and structure.
Other vulnerabilities in MDEx
See all- CVE-2026-53428Medium
A vulnerability in the mdex and mdex_native libraries allows an unauthenticated attacker to cause a denial of service via unbounded memory allocation. The parse_highlight_lines function in the LumisAdapter component expands a user-controlled line range from a fenced code block without an upper bound, allocating huge vectors. A payload with a range like 1-2000000000 can exhaust host memory and abort the BEAM process.
- CVE-2026-53427Low
A cross-site scripting (XSS) vulnerability was found in the MDEx library due to improper input neutralization in Markdown processing. An attacker can inject arbitrary HTML/JavaScript that executes in the browser of every user viewing the rendered output.
- CVE-2026-54889Medium
XSS vulnerability in the mdex library for Elixir allows an attacker to inject JavaScript code via improper validation of URL schemes in Markdown to Quill Delta processing. An attacker can supply a malicious link with javascript: scheme in Markdown text, which is copied verbatim to the Delta attribute and executed in the victim's browser when rendered to HTML.
- CVE-2026-54888Medium
A vulnerability in the mdex library (and mdex_native) allows a DoS attack by supplying a deeply nested Markdown document. Recursive conversion functions lack a maximum depth check, causing a C stack overflow and crashing the entire BEAM node.
- CVE-2026-53429Medium
A missing release of memory after effective lifetime vulnerability in mdex and mdex_native allows an attacker who controls a rendered document to cause a denial of service through unbounded native memory exhaustion. The native rendering code permanently leaks memory when rendering a document containing escaped-tag nodes, leading to unlimited memory consumption and process crash.
Original NVD description (English source)
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.