CVE-2026-106558: Backstage Improper Validation Of TechDocs MkDocs Vulnerability

HIGH
Advisory Identifier: GHSA-qmw3-745m-w99g
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CVSS 8.8
CWE-502
Published
Advisory Summary

CVE-2026-106558 is a HIGH (CVSS 8.8) improper validation of techdocs mkdocs vulnerability (CWE-502: Deserialization of Untrusted Data) affecting Backstage libraries in the npm ecosystem. The issue involves improper validation of techdocs mkdocs configuration. Remediation is available by upgrading affected packages to version 1.15.4.

CVE-2026-106558 at a Glance

CVE Identifier CVE-2026-106558
GHSA Identifier GHSA-qmw3-745m-w99g
Severity HIGH
CVSS v3.1 Base Score 8.8
CWE Classification CWE-502: Deserialization of Untrusted Data
Affected Product Backstage
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 8.8

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2026-106558

To remediate this vulnerability, upgrade all affected Backstage dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

@backstage/plugin-techdocs-node fixed: 1.15.4 
npm install @backstage/plugin-techdocs-node@1.15.4
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls @backstage/plugin-techdocs-node

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-106558, inspect your project dependencies using npm:

npm ls @backstage/plugin-techdocs-node

Analyze the terminal output to locate any version of Backstage in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.15.4), your application is affected.

Note: The npm ls @backstage/plugin-techdocs-node command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-502: Deserialization of Untrusted Data, where the product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid. In Backstage, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact An attacker who can provide configuration to a TechDocs build may execute code in the generator runtime. Impact is greatest when documentation generation runs with backend credentials or host access. ### Patches Patched in `@backstage/plugin-techdocs-node` version `1.15.4`. ### Workarounds Use external TechDocs generation in an isolated environment without sensitive credentials or host access. Restrict and review changes to documentation configuration before generation.

CVE-2026-106558 Affected Backstage Versions

1 component(s)
Fixed Versions:
1.15.4
Product / Package Ecosystem Affected Versions Fixed Version
@backstage/plugin-techdocs-node
npm/@backstage/plugin-techdocs-node
npm
< 1.15.4
1.15.4

References

GitHub Advisory / Wiki ADVISORY
https://github.com/backstage/backstage/security/advisories/GHSA-qmw3-745m-w99g
NVD — CVE-2026-106558 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-106558
Security Fix Commit FIX COMMIT
https://github.com/backstage/backstage/commit/32723a0fe4e12ed80535fc65d5331765c55aa91b
Security Fix Commit FIX COMMIT
https://github.com/backstage/backstage/commit/944edb51c8524d3664b18f2d57ba101b1c93b709
Security Fix Commit FIX COMMIT
https://github.com/backstage/backstage/commit/f18e9abcc6051491862b15e4fc60e69f8d52310c
Backstage Source Repository REPOSITORY
https://github.com/backstage/backstage
Backstage Release RELEASE
https://github.com/backstage/backstage/releases/tag/v1.50.7
Backstage Release RELEASE
https://github.com/backstage/backstage/releases/tag/v1.54.9
Backstage Release RELEASE
https://github.com/backstage/backstage/releases/tag/v1.55.2

Frequently Asked Questions

What is CVE-2026-106558?
CVE-2026-106558 is a security vulnerability in Backstage involving Improper validation of TechDocs MkDocs configuration under CWE-502: Deserialization of Untrusted Data.
Which Backstage versions are affected?
Affected versions include releases prior to 1.15.4 across affected packages: @backstage/plugin-techdocs-node.
What version fixes CVE-2026-106558?
Upgrading to 1.15.4 (or the latest patched release for your respective branch) resolves the vulnerability.
Is @backstage/plugin-techdocs-node affected?
Yes, @backstage/plugin-techdocs-node is affected in releases prior to 1.15.4. Upgrade your dependency to 1.15.4 or later.
What is the CVSS score of CVE-2026-106558?
CVE-2026-106558 has a CVSS v3.1 base score of 8.8 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2026-106558?
CVE-2026-106558 is classified under CWE-502: Deserialization of Untrusted Data (The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.).
How can I check npm dependencies for CVE-2026-106558?
Run the dependency tree command: 'npm ls @backstage/plugin-techdocs-node'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-qmw3-745m-w99g",
  "modified" : "2026-10-07T18:03:12Z",
  "published" : "2026-10-07T18:03:12Z",
  "aliases" : [ "CVE-2026-106558" ],
  "summary" : "Backstage: Improper validation of TechDocs MkDocs configuration",
  "details" : "### Impact\n\nAn attacker who can provide configuration to a TechDocs build may execute code in the generator runtime. Impact is greatest when documentation generation runs with backend credentials or host access.\n\n### Patches\n\nPatched in `@backstage/plugin-techdocs-node` version `1.15.4`.\n\n### Workarounds\n\nUse external TechDocs generation in an isolated environment without sensitive credentials or host access. Restrict and review changes to documentation configuration before generation.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@backstage/plugin-techdocs-node"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.15.4"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/backstage/backstage/security/advisories/GHSA-qmw3-745m-w99g"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-106558"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/backstage/backstage/commit/32723a0fe4e12ed80535fc65d5331765c55aa91b"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/backstage/backstage/commit/944edb51c8524d3664b18f2d57ba101b1c93b709"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/backstage/backstage/commit/f18e9abcc6051491862b15e4fc60e69f8d52310c"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/backstage/backstage"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/backstage/backstage/releases/tag/v1.50.7"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/backstage/backstage/releases/tag/v1.54.9"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/backstage/backstage/releases/tag/v1.55.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-502" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-07T18:03:12Z",
    "nvd_published_at" : "2026-10-07T15:17:15Z"
  }
}