Exploitation requires the application to enable code-block decorators. Decorators are active only when the render options github_pre_lang and full_info_string are both set and an inline syntax-highlight formatter (for example {:html_inline, ...}) is configured. Applications that render Markdown with the default options do not parse highlight_lines specifications and are not affected.
" } ], "value": "Exploitation requires the application to enable code-block decorators. Decorators are active only when the render options github_pre_lang and full_info_string are both set and an inline syntax-highlight formatter (for example {:html_inline, ...}) is configured. Applications that render Markdown with the default options do not parse highlight_lines specifications and are not affected." } ], "cpeApplicability": [ { "nodes": [ { "cpeMatch": [ { "criteria": "cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:*", "versionEndExcluding": "0.12.3", "versionStartIncluding": "0.11.0", "vulnerable": true } ], "negate": false, "operator": "AND" }, { "cpeMatch": [ { "criteria": "cpe:2.3:a:leandrocp:mdex_native:*:*:*:*:*:*:*:*", "versionEndExcluding": "0.2.3", "versionStartIncluding": "0.1.0", "vulnerable": true } ], "negate": false, "operator": "AND" } ], "operator": "OR" } ], "credits": [ { "lang": "en", "type": "finder", "value": "Peter Ullrich" }, { "lang": "en", "type": "remediation developer", "value": "Leandro Pereira" }, { "lang": "en", "type": "analyst", "value": "Jonatan Männchen / EEF" } ], "descriptions": [ { "lang": "en", "supportingMedia": [ { "base64": false, "type": "text/html", "value": "Memory Allocation with Excessive Size Value vulnerability in leandrocp mdex allows an unauthenticated attacker to cause a denial of service through unbounded memory allocation.comrak_nif::lumis_adapter::LumisAdapter::parse_highlight_lines in native/comrak_nif/src/lumis_adapter.rs eagerly expands a user-controlled inclusive line range from a fenced code block's highlight_lines decorator into a Vec<usize>, pushing one element per integer in the range with no upper bound on the range size. An attacker who can supply Markdown that an application renders with MDEx.to_html/2 (for example a comment, chat message, or wiki page) can embed a code block whose info string is rust highlight_lines=\"1-100000000\", forcing the native adapter to allocate roughly 8 bytes per line in the range.
A payload that differs by only a few bytes can therefore allocate hundreds of megabytes, and a sufficiently large range (for example 1-2000000000) exhausts host memory and aborts the BEAM, denying service to every user of the rendering process. The per-line write loop additionally tests membership with a linear scan over the same vector, degrading rendering to a quadratic cost even for ranges that do not immediately exhaust memory.
The vulnerable native code originally shipped inside mdex (in native/comrak_nif/src/lumis_adapter.rs) and was later extracted into the separate mdex_native package (native/mdex_native_nif/src/lumis_adapter.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.
" } ], "value": "Memory Allocation with Excessive Size Value vulnerability in leandrocp mdex allows an unauthenticated attacker to cause a denial of service through unbounded memory allocation.\n\ncomrak_nif::lumis_adapter::LumisAdapter::parse_highlight_lines in native/comrak_nif/src/lumis_adapter.rs eagerly expands a user-controlled inclusive line range from a fenced code block's highlight_lines decorator into a VecDo not enable code-block decorators: leave the github_pre_lang and full_info_string render options unset, or avoid configuring an inline syntax-highlight formatter, so that highlight_lines specifications are never parsed.
" } ], "value": "Do not enable code-block decorators: leave the github_pre_lang and full_info_string render options unset, or avoid configuring an inline syntax-highlight formatter, so that highlight_lines specifications are never parsed." } ], "x_generator": { "engine": "cvelib 1.8.0" } }, "adp": [ { "metrics": [ { "other": { "type": "ssvc", "content": { "timestamp": "2026-06-29T19:17:11.005816Z", "id": "CVE-2026-53428", "options": [ { "Exploitation": "none" }, { "Automatable": "no" }, { "Technical Impact": "partial" } ], "role": "CISA Coordinator", "version": "2.0.3" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-06-29T19:17:25.070Z" } } ] } }