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.

AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/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

CWE-789

https://cna.erlef.org/cves/CVE-2026-53428.html

https://github.com/leandrocp/mdex_native/commit/798a363b4339f6f7162ec8437c4c9f9b5ae6fbf3

https://github.com/leandrocp/mdex_native/security/advisories/GHSA-j93q-9cvj-rxfm

https://osv.dev/vulnerability/EEF-CVE-2026-53428

[{"vendor":"leandrocp","product":"mdex","defaultStatus":"unaffected","collectionURL":"https://repo.hex.pm","packageName":"mdex","cpes":["cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MDEx'","comrak_nif"],"programFiles":["native/comrak_nif/src/lumis_adapter.rs"],"programRoutines":[{"name":"comrak_nif::lumis_adapter::LumisAdapter::parse_highlight_lines"},{"name":"'Elixir.MDEx':to_html/2"}],"repo":"https://github.com/leandrocp/mdex","packageURL":"pkg:hex/mdex","versions":[{"version":"0.11.0","lessThan":"0.12.3","versionType":"semver","status":"affected"}]},{"vendor":"leandrocp","product":"mdex","defaultStatus":"unaffected","collectionURL":"https://github.com","packageName":"leandrocp/mdex","cpes":["cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MDEx'","comrak_nif"],"programFiles":["native/comrak_nif/src/lumis_adapter.rs"],"programRoutines":[{"name":"comrak_nif::lumis_adapter::LumisAdapter::parse_highlight_lines"},{"name":"'Elixir.MDEx':to_html/2"}],"repo":"https://github.com/leandrocp/mdex","packageURL":"pkg:github/leandrocp/mdex","versions":[{"version":"a8407611715d1ead35fbcba79c72cef1b7df387b","lessThan":"6ed94d905f97af188323f042698ae841c02293b4","versionType":"git","status":"affected"}]},{"vendor":"leandrocp","product":"mdex_native","defaultStatus":"unaffected","collectionURL":"https://repo.hex.pm","packageName":"mdex_native","cpes":["cpe:2.3:a:leandrocp:mdex_native:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MDExNative.Comrak'","mdex_native_nif"],"programFiles":["native/mdex_native_nif/src/lumis_adapter.rs"],"programRoutines":[{"name":"mdex_native_nif::lumis_adapter::LumisAdapter::parse_highlight_lines"},{"name":"'Elixir.MDExNative.Native':document_to_html_with_options/2"},{"name":"'Elixir.MDExNative.Comrak':document_to_html/2"}],"repo":"https://github.com/leandrocp/mdex_native","packageURL":"pkg:hex/mdex_native","versions":[{"version":"0.1.0","lessThan":"0.2.3","versionType":"semver","status":"affected"}]},{"vendor":"leandrocp","product":"mdex_native","defaultStatus":"unaffected","collectionURL":"https://github.com","packageName":"leandrocp/mdex_native","cpes":["cpe:2.3:a:leandrocp:mdex_native:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MDExNative.Comrak'","mdex_native_nif"],"programFiles":["native/mdex_native_nif/src/lumis_adapter.rs"],"programRoutines":[{"name":"mdex_native_nif::lumis_adapter::LumisAdapter::parse_highlight_lines"},{"name":"'Elixir.MDExNative.Native':document_to_html_with_options/2"},{"name":"'Elixir.MDExNative.Comrak':document_to_html/2"}],"repo":"https://github.com/leandrocp/mdex_native","packageURL":"pkg:github/leandrocp/mdex_native","versions":[{"version":"956528c5e31746253347029e810a969ab916fd27","lessThan":"798a363b4339f6f7162ec8437c4c9f9b5ae6fbf3","versionType":"git","status":"affected"}]}]