Uncontrolled recursion over deeply nested Markdown crashes the BEAM in mdex

Summary

CVE	CVE-2026-54888
State	PUBLISHED
Assigner	EEF
Source Priority	CVE Program / NVD first with legacy fallback
Published	2026-06-29 20:17:39 UTC
Updated	2026-06-30 14:14:35 UTC
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.

Risk And Classification

Primary CVSS: v4.0 6.9 MEDIUM from 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS: 0.001680000 probability, percentile 0.063880000 (date 2026-06-30)

Problem Types: CWE-674 | CWE-674 CWE-674 Uncontrolled Recursion

Version	Source	Type	Score	Severity	Vector
4.0	6b3ad84c-e1a6-4bf7-a703-f496b71e49db	Secondary	6.9	MEDIUM	`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/E:X/C...`
4.0	CNA	CVSS	6.9	MEDIUM	`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`

CVSS v4.0 Breakdown

Attack Vector

Local

Attack Complexity

Low

Attack Requirements

None

Privileges Required

None

User Interaction

None

Confidentiality

None

Integrity

None

Availability

High

Sub Conf.

None

Sub Integrity

None

Sub Availability

None

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Vendor Declared Affected Products

Source	Vendor	Product	Version	Platforms
CNA	Leandrocp	Mdex	affected 0.3.0 0.12.3 semver	Not specified
CNA	Leandrocp	Mdex	affected d0bc7d55177727c61d188ef465178ab3b81f4f2c 6ed94d905f97af188323f042698ae841c02293b4 git	Not specified
CNA	Leandrocp	Mdex Native	affected 0.1.0 0.2.3 semver	Not specified
CNA	Leandrocp	Mdex Native	affected 956528c5e31746253347029e810a969ab916fd27 947696c47bc22bea5dffc0f78c946fa6b70ce183 git	Not specified

References

Reference	Source	Link	Tags
osv.dev/vulnerability/EEF-CVE-2026-54888	6b3ad84c-e1a6-4bf7-a703-f496b71e49db	osv.dev
cna.erlef.org/cves/CVE-2026-54888.html	6b3ad84c-e1a6-4bf7-a703-f496b71e49db	cna.erlef.org
github.com/leandrocp/mdex_native/commit/947696c47bc22bea5dffc0f78c946fa6...	6b3ad84c-e1a6-4bf7-a703-f496b71e49db	github.com
github.com/leandrocp/mdex_native/security/advisories/GHSA-3w4f-53g2-f66p	134c704f-9b21-4f2e-91b3-4a467353bcc0	github.com
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Peter Ullrich (en)

CNA: Leandro Pereira (en)

CNA: Jonatan Männchen / EEF (en)

There are currently no legacy QID mappings associated with this CVE.