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.
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-2026-53429Medium
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.
- CVE-2026-53426High
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.
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.