[Solved] Curl: (35) SSL_Connect_Error


Here, I will show you what is SSL_Connect_ Error, what are the causes, and how to troubleshoot it.

Secure Sockets Layer (SSL) serves as the backbone of secure internet communications, providing privacy, integrity, and security for data transmitted between machines.

However, even well-designed systems can encounter issues, and one such problem users may face is the “ssl_connect_error” when using the command-line tool curl.

Let’s find out the solution –

What is The SSL_Connect_Error?

The SSL_Connect_Error, also known as the curl: (35) SSL connect error, is a problem that arises when a server attempts to connect to an SSL website using curl.

This error usually occurs when curl fails to perform the SSL handshake properly with the server​.

Causes of Curl: (35) SSL_Connect_Error

There are several potential reasons why you might encounter this error. The primary cause is often attributed to the outdated curl package on your system. You could be using an old version of curl that has a bug causing this issue​.

Another factor could be related to multi-threading. If curl is used across multiple threads and shared data and handles are not managed properly, you might encounter this error.

Particularly, one might see errors like “sschannel: next initializesecuritycontext failed: SEC_E_MESSAGE_ALTERED” or “sschannel: next initializesecuritycontext failed: SEC_E_BUFFER_SMALL”​.

Solving the SSL_Connect_Error

Updating the Curl Package

The primary solution to this problem is to update the curl package on your system to the latest version.

For instance, if you’re on a system that uses the Advanced Package Tool (APT), you can update curl using the following commands​ –

curl package on your system.\n\n## Solution\n\nTo fix this problem simply update the curl package to the newest version. To do so, run the following command:\n\nCopied!\n\n sudo apt update\n sudo apt upgrade","pub_date":null}}​:

  1. Open a terminal window.
  2. Run the command sudo apt update to update the package list.
  3. Run the command sudo apt upgrade to upgrade all outdated packages.

Updating NSS

Network Security Services (NSS) is a set of libraries designed to support cross-platform development of security-enabled client and server applications. If updating curl does not resolve the issue, you might consider updating NSS as well​.

Manage Threading Properly

If you are using curl across multiple threads, ensure that shared data and handles are thread-safe.

One way to do this is by using mutexes to lock your curl operation, which can prevent other threads from accessing it at the same time.

Alternatively, you can try running your program in single-thread mode to see if the issue persists​.

Use the -k1 Option for Older Curl Versions

For older curl versions, such as curl-7.19.7-46.el6.x86_64, providing the option -k1 (small K1) can help avoid this error​.

Besides these solutions, you might also look into below things –

  • Verify that the server’s SSL certificate is valid, up-to-date, and issued by a trusted CA.
  • Update curl to the latest version, ensuring it supports the latest SSL/TLS protocol versions.
  • Check the server’s configuration and ensure it supports compatible cipher suites with curl.
  • Temporarily disable firewalls or antivirus software to check if they are causing the error.
  • Troubleshoot network connectivity issues or contact your ISP for assistance.


Encountering errors while trying to establish a secure connection can be frustrating. However, understanding the causes and solutions for the SSL_Connect_Error can help you swiftly resolve the problem.

By ensuring you’re using the latest version of curl, properly managing threading, and utilizing correct curl options, you can maintain secure and reliable connections.

Keep your systems updated and monitor the latest discussions on the topic to stay ahead of potential issues.