Description
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.
Published: 2026-06-29
Score: 6.9 Medium
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

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History

Mon, 29 Jun 2026 21:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Mon, 29 Jun 2026 19:30:00 +0000

Type Values Removed Values Added
Description 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.
Title Uncontrolled recursion over deeply nested Markdown crashes the BEAM in mdex
First Time appeared Leandrocp
Leandrocp mdex
Leandrocp mdex Native
Weaknesses CWE-674
CPEs cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:*
cpe:2.3:a:leandrocp:mdex_native:*:*:*:*:*:*:*:*
Vendors & Products Leandrocp
Leandrocp mdex
Leandrocp mdex Native
References
Metrics cvssV4_0

{'score': 6.9, 'vector': 'CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}

Subscriptions

Leandrocp Mdex Mdex Native
cve-icon MITRE

Status: PUBLISHED

Assigner: EEF

Published:

Updated: 2026-06-29T20:47:50.953Z

Reserved: 2026-06-16T10:47:13.915Z

Link: CVE-2026-54888

cve-icon Vulnrichment

Updated: 2026-06-29T20:47:45.481Z

cve-icon NVD

No data.

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-06-29T21:00:04Z

Weaknesses