The error means curl cannot verify the server’s TLS/SSL certificate, so it refuses to create an HTTPS connection to keep things secure. It is most often caused by missing or incorrect CA certificates, self‑signed certificates, or TLS inspection proxies.

What the error really says

When you see:

curl failed to verify the legitimacy of the server and therefore could not establish a secure connection to it. To learn more about this situation and how to fix it, please visit the web page mentioned above.

curl is telling you:

  • “I don’t trust the certificate chain I see from this server.”
  • “Because I can’t trust it, I will not complete the HTTPS handshake.”
  • “If you really want to know the low‑level details, check the URL printed just above (usually a curl docs page like sslcerts.html).”

In other words, the problem is about certificate trust , not about HTTP itself.

Common reasons this happens

Typical root causes include:

  1. Self‑signed or enterprise-intercepted certificates
    • The server (or a corporate proxy like Zscaler) is using a self‑signed or custom CA that your system doesn’t trust by default.
 * You often see messages like “self signed certificate in certificate chain.”
  1. CA bundle on the client is outdated or incomplete
    • The local CA store does not contain the CA that signed the server certificate.
 * This can happen after OS/curl updates or on minimal containers where CA packages were never installed.
  1. Misconfigured server certificate
    • Wrong hostname in the certificate (CN/SAN mismatch).
    • Intermediate certificates not sent by the server, so the chain can’t be built to a trusted root.
  1. Strict new curl / OS security updates
    • A curl or system update tightens TLS checks and suddenly a previously “working” but misconfigured setup starts failing.

Safe ways to fix it (recommended)

You generally want to fix the trust chain , not just turn off verification.

1. Make sure CA certificates are installed and updated

On a typical Linux system:

  • Install/update the CA bundle package (examples):
    • Debian/Ubuntu: ca-certificates
    • CentOS/RHEL/Fedora: ca-certificates
  • Then refresh CA certificates if required (e.g., update-ca-certificates on Debian/Ubuntu) and retry your curl command.

If you are in a container image:

  • Install CA certificates explicitly (many minimal images omit them), then rerun curl.

2. Add your organization’s root CA (for self‑signed / TLS inspection)

If you’re behind a corporate proxy or using your own internal CA:

  • Obtain the root CA certificate (often .cer/.crt) from your IT/PKI team.
  • Place it in the system’s trust store (e.g., /usr/local/share/ca-certificates/ on Debian/Ubuntu) and run the update command (update-ca-certificates).
  • Ensure the web server (or proxy) is serving a full, correct certificate chain.

This lets curl verify the certificate properly without weakening security.

3. Fix server certificate configuration

If you control the server:

  • Confirm the certificate’s Common Name / SAN matches the hostname you use in curl (e.g., api.example.com).
  • Ensure all intermediate certificates are configured on the server so clients can validate the chain.
  • Use a reputable CA (for public sites, Let’s Encrypt or commercial CAs) and test with tools like SSL Labs.

The tempting quick “fix”: disabling verification

curl offers options to skip certificate checks:

  • Command line: curl -k or curl --insecure.
  • C code: curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, FALSE);.

This will usually make the error disappear, because curl no longer verifies the server. But this is risky:

  • You lose protection against man‑in‑the‑middle attacks.
  • You train scripts and teams to accept insecure patterns.
  • Many security baselines explicitly forbid this in production.

This approach is only reasonable in short‑lived, controlled testing where you fully understand the risk and environment.

Practical “what should I do?” paths

If you’re a regular user just trying to run a command

  1. Check if you’re on a company network or VPN.
  2. Ask IT whether an SSL inspection proxy is used and whether you need to install a corporate root CA.
  3. Update your system’s CA certificates and retry curl.
  4. Only use -k as a last resort for temporary debugging.

If you’re a developer or admin

  1. Confirm the server’s certificate chain and hostname with a browser or openssl s_client.
  2. Fix the server configuration (hostname, intermediates, CA) if it’s under your control.
  3. Make sure your container/VM images include and maintain a proper CA bundle.
  4. If you must trust an internal CA, add it to your systems’ trust stores instead of using --insecure.

Mini forum-style perspective

You’ll find this error discussed in many public threads, from package managers (like Homebrew) to imaging tools and corporate environments:

“curl failed to verify the legitimacy of the server… There are options there about asking curl not to need to verify the certificate, I believe? Should I do this?”

Community consensus is:

  • For production and anything sensitive: fix the certificates and trust chain.
  • For quick tests: -k works, but document clearly that it’s a temporary workaround and not a final solution.

SEO-focused extras (as requested in your template)

  • This error appears frequently in latest news around security hardening and curl updates, especially when new CVEs or stricter TLS checks roll out.
  • It is a trending topic on sysadmin and developer forums, because it often breaks automation (CI pipelines, package installs, PXE boot tools) until CA trust is fixed.

Meta description example (for your post):

Learn what “curl failed to verify the legitimacy of the server” means, why curl blocks insecure HTTPS connections, and how to fix certificate and CA issues safely without disabling verification.

Information gathered from public forums or data available on the internet and portrayed here.