The mdex library for Elixir uses two mutually recursive Rust functions in its NIF implementation to convert between Elixir %MDEx.Document{} structs and Comrak's internal AST. These functions, ex_document_to_comrak_ast and comrak_ast_to_ex_document, do not limit recursion depth, allowing an attacker to craft Markdown documents with excessive nesting (e.g., thousands of nested block quotes). This leads to unbounded recursion and stack overflow in native code, causing a SIGSEGV that crashes the BEAM virtual machine process. The crash affects the entire Erlang/Elixir node, not just the invoking process. The vulnerability requires no privileges and can be triggered by any user able to render Markdown via MDEx.parse_document!/1 or MDEx.to_html/1. The issue exists in mdex versions >=0.3.0 and <0.12.3 and in mdex_native >=0.1.0 and <0.2.3.

Exploitation results in a denial of service by crashing the entire BEAM virtual machine process running Elixir and Erlang applications on the affected node. This is due to an uncatchable segmentation fault caused by stack overflow in native code. The impact is high availability disruption, affecting all processes on the node, with no need for authentication or special privileges.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. No official fix or patch is documented in the provided data. Until a patch is available, avoid rendering untrusted Markdown input with mdex or mdex_native versions affected by this vulnerability. Consider applying input validation or limiting recursion depth externally if possible.