CVE-2026-53429

What it is

Missing Release of Memory after Effective Lifetime vulnerability in leandrocp 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 that contains escaped-tag nodes. The conversion of each %MDEx.EscapedTag{} node into its native representation (From<ExEscapedTag> for NodeValue in the Rust NIF) calls Box::leak on the caller-supplied literal string, which surrenders the backing allocation so that it lives for the entire lifetime of the operating system process and is never freed. Both the byte length of each literal and the number of escaped-tag nodes in a document are attacker-controlled, and there is no size cap, rate limit, or string interning on this path. Every render of a document containing escaped-tag nodes therefore leaks literal_size x node_count bytes that can never be reclaimed, and repeated renders accumulate without bound. Rendering reaches this path through the public MDEx.to_html/1 entry point and any other API that renders a supplied %MDEx.Document{}. Any application that uses mdex (or mdex_native directly) to render documents derived from user-supplied content is affected. Because the leaked memory is never reclaimed for the life of the BEAM process, an attacker can drive resident memory upward without limit until the node exhausts memory and crashes, taking down every process on it. The vulnerable native code originally shipped inside mdex (in native/comrak_nif/src/types/document.rs) and was later extracted into the separate mdex_native package (native/mdex_native_nif/src/types/document.rs), where it remains unpatched. This issue affects mdex from 0.11.0 before 0.12.3, and mdex_native from 0.1.0 before 0.2.3.

At a glance

Exploitability

Can be exploited locally on the machine without logging in. High risk of service disruption.

Exploit odds

0.2% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-06-29 20:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-10-25 21:10 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.2% in the next 30 days (EPSS).
• Severity: 6.9 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-06-29 20:17 UTC

Last modified

2026-10-25 21:10 UTC

Exploit probability

0.2% · EPSS, next 30 days

Weakness

CWE-401

Record status

Deferred

Attack profile CVSS 4.0 · 6.9

Attack vector

Local

Complexity

Low

Attack requirements

None

Privileges needed

None

User interaction

None

Confidentiality

None

Integrity

None

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-53429.md and follow it. Check whether this project is affected by CVE-2026-53429. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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