Vikunja: Unbounded nested task-filter recursion permits API process termination

{
  "id": "e3aff975e11f54549144151c7156d9dc0aaeb65f414cd3137a0f9b8423057aa6",
  "url": "https://osv.dev/vulnerability/GHSA-xxc3-xpmc-vmvr",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Vikunja: Unbounded nested task-filter recursion permits API process termination",
    "summary": "# Unbounded nested task-filter recursion permits API process termination ## Summary Authenticated task-list routes accept a filter expression without a length or nesting-depth bound, preprocess it, parse it recursively through fexpr, and recursively convert the resulting expression tree. A syntactically valid deeply nested expression well below the HTTP request-size ceiling exhausts memory and kills the API process. ## Impact and affected scope - **Type:** Resource Exhaustion Recursive Parser - **Affected component:** GET /api/v2/projects/{project}/tasks?filter=; Other authenticated task-collection entrypoints that share getTaskFiltersFromFilterString - **Preconditions:** A low-privileged authenticated user supplies thousands of balanced parentheses around a valid task predicate in the filter query parameter. - **Verified revision:** `349cd5adbcc831ef08b08e6c9c6d627603c39606` on 28 August 2026 - **Affected release range:** `= 2.5.0`; broader historical range not established and maintainer confirmation requested A single low-privileged network request can terminate the API process and deny service to all users. ## Technical details The server preprocesses and recursively parses/traverses an unbounded filter expression without rejecting excessive length or depth. Attack path: Authenticate, request an accessible project's task collection with 20,000 nested parenthesis pairs around id = 1, and drive parser and expression-tree memory growth until the process is killed. Relevant co",
    "evidence": "osv:GHSA-xxc3-xpmc-vmvr",
    "products": [
      {
        "name": {
          "value": "code.vikunja.io/api",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "2.6.0",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": [
          {
            "value": "2.5.0",
            "evidence": "/affected/0/versions"
          }
        ]
      }
    ],
    "severity": "high",
    "structured": {
      "id": "GHSA-xxc3-xpmc-vmvr",
      "aliases": [
        "CVE-2026-91968",
        "GHSA-xxc3-xpmc-vmvr",
        "GO-2026-6759"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "2.5.0"
                },
                {
                  "fixed": "2.6.0"
                }
              ]
            }
          ],
          "package": {
            "name": "code.vikunja.io/api",
            "purl": "pkg:golang/code.vikunja.io/api",
            "ecosystem": "Go"
          },
          "versions": [
            "2.5.0"
          ],
          "database_specific": {
            "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-xxc3-xpmc-vmvr/GHSA-xxc3-xpmc-vmvr.json"
          }
        }
      ],
      "modified": "2026-10-19T21:40:57.352245323Z",
      "provider": "osv",
      "references": [
        "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-xxc3-xpmc-vmvr",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-91968",
        "https://github.com/go-vikunja/vikunja/pull/3688",
        "https://github.com/go-vikunja/vikunja",
        "https://github.com/go-vikunja/vikunja/releases/tag/v2.6.0",
        "https://www.vulncheck.com/advisories/vikunja-before-2.6.0-denial-of-service-via-unbounded-filter-recursion"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-674"
        ],
        "severity": "HIGH",
        "github_reviewed": true,
        "nvd_published_at": null,
        "github_reviewed_at": "2026-10-09T20:53:03Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-91968",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/database_specific/severity"
  },
  "source_id": "core-osv",
  "document_id": 376760,
  "published_at": "2026-10-09T20:53:03+00:00"
}