CVE-2026-54888
MediumCVSS 6.9Exploitation Probability (EPSS)
Low risk6th percentile — higher than 6% of all known CVEs
Summary
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.
Risk Assessment
An unauthenticated attacker can terminate all Elixir/Erlang processes on the node, leading to complete service unavailability. The crash is uncatchable and cannot be handled by the Erlang VM.
Recommendation
Immediately update mdex to version 0.12.3 or later, and mdex_native to version 0.2.3 or later. If updating is not possible, restrict access to Markdown processing functions to trusted users only.
Original NVD description (English source)
Uncontrolled Recursion vulnerability in leandrocp mdex allows denial of service via deeply nested Markdown input. mdex converts between an Elixir %MDEx.Document{} struct and Comrak's internal AST using two mutually recursive Rust functions, ex_document_to_comrak_ast and comrak_ast_to_ex_document, in the NIF source file document.rs. Neither function enforces a maximum nesting depth, so the recursion depth is bounded only by the structure of the input. An attacker who can get a Markdown document rendered (for example through MDEx.parse_document!/1 or MDEx.to_html/1) can supply a document with thousands of nested block quotes, which drives unbounded recursion across the NIF boundary and exhausts the native C stack. Because the resulting stack overflow is an uncatchable SIGSEGV raised inside a NIF, it cannot be contained by the Erlang runtime. It terminates the operating system process running the BEAM, killing every Elixir and Erlang process on the node, not just the caller that triggered the render. No authentication or special privileges are required. The vulnerable conversion code was extracted from mdex into the separate mdex_native package starting in mdex 0.12.3. This issue affects mdex from 0.3.0 before 0.12.3 and mdex_native from 0.1.0 before 0.2.3.