CVE-2026-29794: Code.vikunja.io/api Vikunja Has A Rate-Limit Bypass Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-m547-hp4w-j6jx",
  "modified" : "2026-03-20T21:28:21Z",
  "published" : "2026-03-20T14:41:03Z",
  "aliases" : [ "CVE-2026-29794" ],
  "summary" : "Vikunja has a Rate-Limit Bypass for Unauthenticated Users via Spoofed Headers",
  "details" : "### Summary\nUnauthenticated users are able to bypass the application's built-in rate-limits by spoofing the `X-Forwarded-For` or `X-Real-IP` headers due to the rate-limit relying on the value of `(echo.Context).RealIP`. \n\n### Details\nIn the first file below, the rate-limit for unauthenticated users can be observed being populated with the `ip` value. In the second file, it shows it using the `c.RealIP()` function for the `ip` case. Due to this, the rate-limit will rely on the value of one of the two mentioned headers (`X-Forwarded-For` or `X-Real-IP`). These can be spoofed by users client-side in order to completely bypass any unauthenticated rate-limits in place.\n\nSome reverse proxies like Traefik will overwrite this value by default, but others will not, leaving any deployment that either isn't using a reserve proxy that specifically overwrites the header's value or isn't using a reverse proxy vulnerable. \n\n**File 1:** pkg\\routes\\routes.go:318\n```go\n// This is the group with no auth\n\t// It is its own group to be able to rate limit this based on different heuristics\n\tn := a.Group(\"\")\n\tsetupRateLimit(n, \"ip\")\n\n\t// Docs\n\tn.GET(\"/docs.json\", apiv1.DocsJSON)\n\tn.GET(\"/docs\", apiv1.RedocUI)\n\n\t// Prometheus endpoint\n\tsetupMetrics(n)\n\n\t// Separate route for unauthenticated routes to enable rate limits for it\n\tur := a.Group(\"\")\n\trate := limiter.Rate{\n\t\tPeriod: 60 * time.Second,\n\t\tLimit:  config.RateLimitNoAuthRoutesLimit.GetInt64(),\n\t}\n\trateLimiter := createRateLimiter(rate)\n\tur.Use(RateLimit(rateLimiter, \"ip\"))\n```\n**File 2:** pkg\\routes\\rate_limit.go:41\n```go\n// RateLimit is the rate limit middleware\nfunc RateLimit(rateLimiter *limiter.Limiter, rateLimitKind string) echo.MiddlewareFunc {\n\treturn func(next echo.HandlerFunc) echo.HandlerFunc {\n\t\treturn func(c *echo.Context) (err error) {\n\t\t\tvar rateLimitKey string\n\t\t\tswitch rateLimitKind {\n\t\t\tcase \"ip\":\n\t\t\t\trateLimitKey = c.RealIP()\n\t\t\tcase \"user\":\n\t\t\t\tauth, err := auth2.GetAuthFromClaims(c)\n\t\t\t\tif err != nil {\n\t\t\t\t\tlog.Errorf(\"Error getting auth from jwt claims: %v\", err)\n\t\t\t\t}\n\t\t\t\trateLimitKey = \"user_\" + strconv.FormatInt(auth.GetID(), 10)\n\t\t\tdefault:\n\t\t\t\tlog.Errorf(\"Unknown rate limit kind configured: %s\", rateLimitKind)\n\t\t\t}\n```\n\n### PoC\n1. Download and run the default docker compose file via the instructions here: [https://vikunja.io/install/](https://vikunja.io/install/). Do not configure a proxy.\n2. Once running, navigate to the application in a web browser that is using a web proxy, such as Burp Suite.\n3. Attempt to authenticate to the application with an invalid username and password.\n4. In the web proxy's logs, locate the request to the `/api/v1/login` endpoint. Observe that the response contains rate-limit details:\n```http\nHTTP/1.1 403 Forbidden\nCache-Control: no-store\nContent-Type: application/json\nVary: Origin\nX-Ratelimit-Limit: 10\nX-Ratelimit-Remaining: 9\nX-Ratelimit-Reset: 1772224455\nDate: Fri, 27 Feb 2026 20:33:16 GMT\nContent-Length: 54\n\n{\"code\":1011,\"message\":\"Wrong username or password.\"}\n```\n5. Add the `X-Forwarded-For` header with an arbitrary value, like so: `X-Forwarded-For: FakeValue`. Send the request 10 times, or until the rate-limit is at zero.\n6. Modify the `X-Forwarded-For` headers value to be different, like so: `X-Forwarded-For: NewValue`.\n7. Observe that the `X-Ratelimit-Remaining` header's value has reset its countdown and is back at `9`. \n\n### Impact\nUnauthenticated users can abuse endpoints available to them for different potential impacts. The immediate concern would be brute-forcing usernames or specific accounts' passwords. This bypass allows unlimited requests against unauthenticated endpoints.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "code.vikunja.io/api"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.8"
      }, {
        "fixed" : "2.2.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-m547-hp4w-j6jx"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-29794"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/go-vikunja/vikunja/commit/a498dd69915a006c07e9d82660a2185d7e8136ee"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/go-vikunja/vikunja"
  }, {
    "type" : "WEB",
    "url" : "https://vikunja.io/changelog/vikunja-v2.2.0-was-released"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-807" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-20T14:41:03Z",
    "nvd_published_at" : "2026-03-20T15:16:16Z"
  }
}