CVE-2026-43976: wger: cross-tenant admin notes/contracts leak via gym=None bypass (5 views)

Summary

Five gym management views in wger apply a flawed gym-scope guard (gyma != gymb) that silently passes when both operands are None. A trainer with gym.gymtrainer and gym.addadminusernote permissions and no gym assignment (gym=None) can read private admin notes, uploaded documents, gym contracts, user configuration, and user permission data for any other unaffiliated user on the instance. The subsequent querysets filter only on the attacker-supplied memberid with no secondary gym-scoped validation, so all records are disclosed.

Details

Files: wger/gym/views/user.py, wger/gym/views/adminnotes.py, wger/gym/views/document.py, wger/gym/views/contract.py, wger/gym/views/userconfig.py

The same flawed comparison pattern appears across at least five views:

python VULNERABLE - applied in adminnoteslist, documentslist, contractslist, userconfig, and gympermissionsuseredit if request.user.userprofile.gym != user.userprofile.gym: return HttpResponseForbidden()

After the guard (admin notes example): notes = AdminUserNote.objects.filter(member=member) # only filtered by memberid

When both request.user.userprofile.gym and user.userprofile.gym are None, Python evaluates None != None as False, and HttpResponseForbidden is never reached. The subsequent queryset applies only the attacker-supplied member (user ID) as a filter — there is no secondary check tying the queryset to the requesting trainer's gym. All private admin notes, documents, and contracts for the target user are returned in the response body.

Affected endpoints: - GET /en/gym/notes/list/user/<memberpk> -> admin notes list view - GET /en/gym/documents/list/user/<memberpk> -> documents list view - GET /en/gym/contract/list/<memberpk> -> contracts list view - GET /en/gym/user/<memberpk>/config -> user config view - GET /en/gym/user/<memberpk>/permissions -> permission edit view

Suggested patch:

diff --- a/wger/gym/views/user.py +++ b/wger/gym/views/user.py - if request.user.userprofile.gym != user.userprofile.gym: - return HttpResponseForbidden() + trainergymid = request.user.userprofile.gymid + membergymid = user.userprofile.gymid + + if trainergymid is None or trainergymid != membergymid: + return HttpResponseForbidden()

Also tighten the queryset with a gym-scoped secondary filter: - notes = AdminUserNote.objects.filter(member=member) + notes = AdminUserNote.objects.filter( + member=member, + memberuserprofilegymid=request.user.userprofile.gymid, + )

Extract a shared helper assertsamegym(trainer, member) and call it consistently from all five affected views to eliminate future drift.

PoC

Tested on wger/server:latest Docker image. Test users: trainer1 (gym.gymtrainer + gym.addadminusernote permissions, userprofile.gym=None) and alice (regular user, userprofile.gym=None, has a private admin note pre-seeded).

Step 1 - Authenticate as trainer with required perms and gym=None:

POST /en/user/login HTTP/1.1 Host: target Content-Type: application/x-www-form-urlencoded

username=trainer1&password=[REDACTED]&csrfmiddlewaretoken=[REDACTED]

-> 302 Found; Set-Cookie: sessionid=[trainer1session]

Step 2 - Read victim's private admin notes:

GET /en/gym/notes/list/user/2 HTTP/1.1 Host: target Cookie: sessionid=[trainer1session]

-> 200 OK body contains all private admin notes for user 2: "PRIVATENOTEABOUTALICESALARY50K" "PHASE4SECRETSALARY100K"

Step 3 - Read victim's documents and contracts (same pattern):

GET /en/gym/documents/list/user/2 GET /en/gym/contract/list/2

-> 200 OK for each; all records disclosed

Step 4 (optional) - Mass enumeration across all gym=None users:

Iterate user PKs 1..N: GET /en/gym/notes/list/user/{uid} -> 200 = gym=None victim (notes leaked) -> 403 = gym-assigned user (check works correctly when gym values differ)

RBAC Disproof Protocol: - Scenario A (admin, gym=1 -> member gym=1) -> HTTP 200 (expected - same-gym read is a documented feature) - Scenario B (trainer1, gym=None -> alice gym=None) -> HTTP 200 with PII in body (expected HTTP 403) - Scenario C (admin, gym=1 -> alice gym=None) -> HTTP 403 (expected - guard works when gyms differ; confirms bypass is None-specific)

Reproducibility: 2/2 runs after clean-baseline database reset.

Impact

An authenticated trainer with gym.gymtrainer + gym.addadminusernote permissions and userprofile.gym=None can:

1. Enumerate and read all private admin notes for every other gym=None user (notes may contain salary data, medical notes, disciplinary records). 2. Download all uploaded documents attached to those users (contracts, ID scans, medical forms). 3. Read all gym contracts (financial terms, subscription details). 4. Read user configuration details. 5. Via the permissions endpoint, potentially modify victim permissions (creates a privilege escalation path - not fully explored in this submission but the endpoint is reachable).

Affected deployments: every wger instance where gym.gymtrainer + gym.addadminusernote are delegated to non-admin users AND any other users exist with gym=None. The gym=None state is the default for newly registered users before manual gym assignment, so every public-registration wger instance is affected.

Severity: High (CVSS 7.1). Network-reachable, low complexity, requires only low privilege (delegated trainer), scope unchanged (same wger authority), high confidentiality loss across all unaffiliated accounts, low integrity impact (permission-edit view reachable).

This is structurally the same bug class as the sibling findings affecting trainerlogin and resetuserpassword (submitted separately). The root cause - Django ORM object-!= returning False when both sides are None - warrants a shared samegym() helper applied across all five views.