CVE-2026-42267: Kimai/kimai Kimai Vulnerable To Formula Injection Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-3xc2-h5r3-wv3r",
  "modified" : "2026-05-14T20:31:08Z",
  "published" : "2026-05-05T20:53:38Z",
  "aliases" : [ "CVE-2026-42267" ],
  "summary" : "Kimai vulnerable to formula Injection via tag names in XLSX export",
  "details" : "## Summary\n\nAny `ROLE_USER` can create a tag with a formula string as its name (e.g. `=SUM(54+51)`) via `POST /api/tags` and assign it to a timesheet. When an admin exports timesheets to XLSX, `ArrayFormatter.formatValue()` joins tag names with `implode()` and returns the result unchanged. OpenSpout promotes any `=`-prefixed string to a `FormulaCell`, writing `<f>SUM(54+51)</f>` into the XLSX archive. Excel evaluates the formula when the file is opened.\n\n## Details\n\n### 1. `ArrayFormatter` does not sanitize before returning\n\n`sanitizeDDE()` exists on `StringHelper` and is called by `TextFormatter`, but `ArrayFormatter` never calls it.\n```php\n// src/Export/Package/CellFormatter/ArrayFormatter.php:24\nreturn implode(', ', $value);  // no sanitizeDDE() call\n```\n\n### 2. Tag name validation does not block formula trigger characters\n\nThe API blocks commas in tag names but permits `=`, `+`, `-`, and `@` - all valid formula prefixes in Excel and LibreOffice Calc.\n\n### 3. OpenSpout silently promotes strings to formula cells\n\n`Cell::fromValue(\"=SUM(54+51)\")` returns a `FormulaCell` with no warning.\n\n### PoC\n\n1. It logs in as normal user, creates tag `=SUM(54+51)`, assigns it to a timesheet.\n2. Admin has to export timesheets to Excel version via `/en/export/` endpoint.\n\n<img width=\"1339\" height=\"700\" alt=\"image\" src=\"https://github.com/user-attachments/assets/884c7943-5e3b-4647-8bcc-e264d6719d66\" />\n\n<img width=\"1304\" height=\"128\" alt=\"formula_injection_tags\" src=\"https://github.com/user-attachments/assets/ef28f2ad-7491-4a15-bb18-1fcd6ff5e55a\" />\n\n## Impact\n\n- Any `ROLE_USER` can plant a formula that executes on the workstation of any user who exports and opens timesheet data\n- A single malicious tag poisons all future exports across all users and date ranges until the tag is deleted\n\n## Fixes\n\n1. Prevent `=` being part of the tag name (and other fields as well)\n2. Use OpenSpout `TextCell` for everything that is a string",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:H/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:A/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "kimai/kimai"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.27.0"
      }, {
        "fixed" : "2.54.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.53.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/kimai/kimai/security/advisories/GHSA-3xc2-h5r3-wv3r"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-42267"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/kimai/kimai"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/kimai/kimai/releases/tag/2.54.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1236" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-05T20:53:38Z",
    "nvd_published_at" : "2026-05-08T04:16:20Z"
  }
}