CVE-2026-53429 — Unbounded native memory leak in mdex escaped-tag rendering enables unauthenticated denial of service
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.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.2% (30-day exploitation probability)+1
- Technical severity (medium)+3
- CISA SSVC: exploitation "poc"+5
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Leandrocp Mdex, Leandrocp Mdex Native).
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Leandrocp | Mdex | ≥ 0.11.0 and < 0.12.3≥ 81e4d14dd3aa5b206e395c7f372b9b413793015f and < 6ed94d905f97af188323f042698ae841c02293b4 | Vulnerable | CVE Program (cve.org) e CISA ADP |
| Leandrocp | Mdex Native | ≥ 0.1.0 and < 0.2.3≥ 956528c5e31746253347029e810a969ab916fd27 and < cbd927fb5061b488de8d90a8ef6df65718ca1fe6 | Vulnerable | CVE Program (cve.org) e CISA ADP |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 6.9 | CVSS 4.0 | Medium | — | — | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db via NIST National Vulnerability Database |
| 6.9 | CVSS 4.0 | Medium | — | — | EEF via CVE Program (cve.org) e CISA ADP |
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 (score shown at the top: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
CWE-401 · Missing Release of Memory after Effective Lifetime
EPSS over time FIRST
Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.18%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
- Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · leandrocp/mdex, leandrocp/mdex native
- SSVC assessment updated
- Record published
- CVSS changed · 6.9
- Source status changed · → Deferred
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× Official description updated · Oct 13, 2026 – Oct 13, 2026
References
4 on the record
Elsewhere on this site
Related CVEs (same products)
- Medium CVE-2026-54889 Unsanitized URL schemes in MDEx Quill Delta output allow javascript: injection (XSS) Jun 29, 2026
- Medium CVE-2026-54888 Uncontrolled recursion over deeply nested Markdown crashes the BEAM in mdex Jun 29, 2026
- High CVE-2026-53426 Atom-table exhaustion denial-of-service via JSON parse_document in MDEx Jun 29, 2026
- Low CVE-2026-53427 Cross-site scripting in MDEx via unescaped highlight_lines_class code-fence attribute Jun 29, 2026
- Medium CVE-2026-53428 Unbounded memory allocation in highlight_lines range expansion in mdex Jun 29, 2026
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No fixed version, patch or mitigation documented.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-53429 is "Unbounded native memory leak in mdex escaped-tag rendering enables unauthenticated denial of service", rated Medium. It affects Mdex (Leandrocp); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 6.9 describes technical severity. EPSS 0.18% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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