# 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. - **Severity:** Medium 6.9 (`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`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Local or same network only - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 29 Jun 2026 - **Updated:** 30 Jun 2026 - **Also known as:** EEF-CVE-2026-53429, GHSA-cmvp-gp9f-23xw ## 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 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 (Missing Release of Memory after Effective Lifetime) ## Which versions are affected by CVE-2026-53429? 2 open source packages ship an affected version, including mdex and mdex_native. | Package | Ecosystem | 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. ## Is CVE-2026-53429 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-53429 exists. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-53429 and fix it if it is affected. What it is: 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. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-53429 exists. Affected packages and fixed versions: - mdex (Hex): affected from 0.11.0; fixed in 0.12.3 - mdex_native (Hex): affected from 0.1.0; fixed in 0.2.3 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-53429/ (Markdown: https://insights.sbomify.com/CVE-2026-53429/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53429 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53429 - OSV: https://osv.dev/vulnerability/CVE-2026-53429 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-53429/ Summaries are generated and may contain mistakes; the official description above is the record.