CVE-2026-53427
Cross-site scripting in MDEx via unescaped highlight_lines_class code-fence attribute
Description
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in leandrocp MDEx allows stored or reflected cross-site scripting via attacker-controlled Markdown. When syntax highlighting and full info-string forwarding (render: [full_info_string: true]) are enabled, the Lumis adapter copies the value of a code fence's highlight_lines_class info-string attribute, unescaped, into the class attribute of every rendered line. comrak_nif::lumis_adapter::LumisAdapter::parse_custom_attributes in native/comrak_nif/src/lumis_adapter.rs shlex-parses the info string and stores each key=value pair verbatim, highlight_lines_config pulls highlight_lines_class into the per-line class value, and write_highlighted interpolates that value directly into the class attribute of the per-line <div>. A single-quoted shell token preserves an inner double quote through shlex parsing, so a value such as '"><script>alert(1)</script>' terminates the class attribute early and the markup that follows is emitted as live HTML. An attacker who can submit Markdown (through comments, posts, wiki pages, documentation, or any user-generated content) can inject arbitrary HTML and JavaScript that runs in the browser of every user who views the rendered output, enabling session theft, account takeover, and other client-side attacks. No authentication or special privileges are required. 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 0.11.3 before 0.12.3, and mdex_native from 0.1.0 before 0.2.3.
INFO
Published Date :
June 29, 2026, 7:16 p.m.
Last Modified :
June 29, 2026, 8:17 p.m.
Remotely Exploit :
Yes !
Source :
6b3ad84c-e1a6-4bf7-a703-f496b71e49db
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 4.0 | LOW | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | ||||
| CVSS 4.0 | LOW | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db |
Solution
- Update mdex to version 0.12.3 or later.
- Update mdex_native to version 0.2.3 or later.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-53427.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-53427 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-53427
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-53427 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-53427 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 29, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-53427', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-06-29T19:18:13.166991Z'} -
New CVE Received by 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
Jun. 29, 2026
Action Type Old Value New Value Added Affected [{'cpes': ['cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:*'], 'repo': 'https://github.com/leandrocp/mdex', 'vendor': 'leandrocp', 'modules': ["'Elixir.MDEx'", 'comrak_nif'], 'product': 'mdex', 'versions': [{'status': 'affected', 'version': '0.11.3', 'lessThan': '0.12.3', 'versionType': 'semver'}], 'packageURL': 'pkg:hex/mdex', 'packageName': 'mdex', 'programFiles': ['native/comrak_nif/src/lumis_adapter.rs'], 'collectionURL': 'https://repo.hex.pm', 'defaultStatus': 'unaffected', 'programRoutines': [{'name': 'comrak_nif::lumis_adapter::LumisAdapter::parse_custom_attributes'}, {'name': 'comrak_nif::lumis_adapter::LumisAdapter::highlight_lines_config'}, {'name': 'comrak_nif::lumis_adapter::LumisAdapter::write_highlighted'}, {'name': "'Elixir.MDEx':to_html/2"}]}, {'cpes': ['cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:*'], 'repo': 'https://github.com/leandrocp/mdex', 'vendor': 'leandrocp', 'modules': ["'Elixir.MDEx'", 'comrak_nif'], 'product': 'mdex', 'versions': [{'status': 'affected', 'version': '0d7ffc84ea742e1daf666426814e5bb6d0499433', 'lessThan': '6ed94d905f97af188323f042698ae841c02293b4', 'versionType': 'git'}], 'packageURL': 'pkg:github/leandrocp/mdex', 'packageName': 'leandrocp/mdex', 'programFiles': ['native/comrak_nif/src/lumis_adapter.rs'], 'collectionURL': 'https://github.com', 'defaultStatus': 'unaffected', 'programRoutines': [{'name': 'comrak_nif::lumis_adapter::LumisAdapter::parse_custom_attributes'}, {'name': 'comrak_nif::lumis_adapter::LumisAdapter::highlight_lines_config'}, {'name': 'comrak_nif::lumis_adapter::LumisAdapter::write_highlighted'}, {'name': "'Elixir.MDEx':to_html/2"}]}, {'cpes': ['cpe:2.3:a:leandrocp:mdex_native:*:*:*:*:*:*:*:*'], 'repo': 'https://github.com/leandrocp/mdex_native', 'vendor': 'leandrocp', 'modules': ["'Elixir.MDExNative.Comrak'", 'mdex_native_nif'], 'product': 'mdex_native', 'versions': [{'status': 'affected', 'version': '0.1.0', 'lessThan': '0.2.3', 'versionType': 'semver'}], 'packageURL': 'pkg:hex/mdex_native', 'packageName': 'mdex_native', 'programFiles': ['native/mdex_native_nif/src/lumis_adapter.rs'], 'collectionURL': 'https://repo.hex.pm', 'defaultStatus': 'unaffected', 'programRoutines': [{'name': 'mdex_native_nif::lumis_adapter::LumisAdapter::parse_custom_attributes'}, {'name': 'mdex_native_nif::lumis_adapter::LumisAdapter::highlight_lines_config'}, {'name': 'mdex_native_nif::lumis_adapter::LumisAdapter::write_highlighted'}, {'name': "'Elixir.MDExNative.Native':document_to_html_with_options/2"}, {'name': "'Elixir.MDExNative.Comrak':document_to_html/2"}]}, {'cpes': ['cpe:2.3:a:leandrocp:mdex_native:*:*:*:*:*:*:*:*'], 'repo': 'https://github.com/leandrocp/mdex_native', 'vendor': 'leandrocp', 'modules': ["'Elixir.MDExNative.Comrak'", 'mdex_native_nif'], 'product': 'mdex_native', 'versions': [{'status': 'affected', 'version': '956528c5e31746253347029e810a969ab916fd27', 'lessThan': '798a363b4339f6f7162ec8437c4c9f9b5ae6fbf3', 'versionType': 'git'}], 'packageURL': 'pkg:github/leandrocp/mdex_native', 'packageName': 'leandrocp/mdex_native', 'programFiles': ['native/mdex_native_nif/src/lumis_adapter.rs'], 'collectionURL': 'https://github.com', 'defaultStatus': 'unaffected', 'programRoutines': [{'name': 'mdex_native_nif::lumis_adapter::LumisAdapter::parse_custom_attributes'}, {'name': 'mdex_native_nif::lumis_adapter::LumisAdapter::highlight_lines_config'}, {'name': 'mdex_native_nif::lumis_adapter::LumisAdapter::write_highlighted'}, {'name': "'Elixir.MDExNative.Native':document_to_html_with_options/2"}, {'name': "'Elixir.MDExNative.Comrak':document_to_html/2"}]}] Added Description Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in leandrocp MDEx allows stored or reflected cross-site scripting via attacker-controlled Markdown. When syntax highlighting and full info-string forwarding (render: [full_info_string: true]) are enabled, the Lumis adapter copies the value of a code fence's highlight_lines_class info-string attribute, unescaped, into the class attribute of every rendered line. comrak_nif::lumis_adapter::LumisAdapter::parse_custom_attributes in native/comrak_nif/src/lumis_adapter.rs shlex-parses the info string and stores each key=value pair verbatim, highlight_lines_config pulls highlight_lines_class into the per-line class value, and write_highlighted interpolates that value directly into the class attribute of the per-line <div>. A single-quoted shell token preserves an inner double quote through shlex parsing, so a value such as '"><script>alert(1)</script>' terminates the class attribute early and the markup that follows is emitted as live HTML. An attacker who can submit Markdown (through comments, posts, wiki pages, documentation, or any user-generated content) can inject arbitrary HTML and JavaScript that runs in the browser of every user who views the rendered output, enabling session theft, account takeover, and other client-side attacks. No authentication or special privileges are required. 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 0.11.3 before 0.12.3, and mdex_native from 0.1.0 before 0.2.3. Added CVSS V4.0 AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/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 Added CWE CWE-79 Added Reference https://cna.erlef.org/cves/CVE-2026-53427.html Added Reference https://github.com/leandrocp/mdex_native/commit/798a363b4339f6f7162ec8437c4c9f9b5ae6fbf3 Added Reference https://github.com/leandrocp/mdex_native/security/advisories/GHSA-v664-pmxr-mxxx Added Reference https://osv.dev/vulnerability/EEF-CVE-2026-53427