CVE-2026-53429 Unbounded native memory leak in mdex escaped-tag rendering enables unauthenticated denial of service
An attacker can cause unbounded memory exhaustion and crash the application by submitting documents with escaped tags to the mdex library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-53429?
CVE-2026-53429 is a medium-severity denial of service vulnerability in leandrocp mdex, published on 29 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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.
Weakness: CWE-401
Which versions are affected by CVE-2026-53429?
2 open source packages ship an affected version, including mdex and mdex_native.
| Package | Affected | Fixed in |
|---|---|---|
mdex Hex | From 0.11.0 | 0.12.3 |
mdex_native Hex | From 0.1.0 | 0.2.3 |
How do I fix CVE-2026-53429?
Upgrade mdex to 0.12.3 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-53429 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-53429 exists.
Sources
Also known as EEF-CVE-2026-53429, GHSA-cmvp-gp9f-23xw.