The ultimate resource for preventing SSL/TLS based attacks.
Welcome to our SSL/TLS Vulnerabilities resource hub! Learn about the six different types of SSL/TLS vulnerabilities and the ideal configurations to patch known issues. Browse our expert guides to get an in-depth description of some of the more common SSL vulnerabilities and what needs to be done to fix them. We’ve even put together a historical timeline of vulnerability breaches as well as some stats on the current state of things currently.
If it’s your first time here, don’t forget to download your copy of our SSL/TLS Best Practices Checklist below:
Download SSL/TLS Best Practices Checklist
Expert Guides
Read deep-dives on Specific SSL/TLS Vulnerabilities and their solutions
SSL/TLS Vulnerabilities Statistics
How vulnerable is the internet to SSL/TLS attacks?
6 SSL/TLS Vulnerability Types and How to Mitigate Them
Click on the arrows below to expand each category for specific examples and their patches.
Protocol Vulnerabilities – These are weaknesses in the design of SSL/TLS protocols themselves — especially older versions.
| Vulnerability | Description |
| SSL 2.0 / SSL 3.0 | Obsolete and insecure; vulnerable to attacks like POODLE. |
| TLS 1.0 / 1.1 | Deprecated due to weak ciphers, lack of forward secrecy. |
| BEAST (TLS 1.0) | Exploits weaknesses in block cipher mode (CBC). |
| CRIME / BREACH | Exploits compression features in SSL/TLS or HTTP. |
🛠️ Mitigation: Disable all versions before TLS 1.2. Use TLS 1.3 if possible.
Cipher Suite Vulnerabilities – Some cipher algorithms are weak or misconfigured, making them easier to break.
| Vulnerable Cipher Type | Status |
| NULL / ANON | Insecure |
| EXPORT | Insecure |
| SSLv2/SSLv3 | Obsolete |
| RC4 | Deprecated |
| DES / 3DES | Deprecated |
| RSA key exchange | No forward secrecy |
| CBC mode (pre-TLS 1.2) | Vulnerable |
| MD5 hashing | Broken |
🛠️ Mitigation: TLS 1.3 Cipher Suites are dramatically simplified and more secure by design. Use:
- TLS_CHACHA20_POLY1305_SHA256 (especially good for mobile)
- TLS_AES_128_GCM_SHA256
- TLS_AES_256_GCM_SHA384
For specific examples of vulnerable cipher suites, click to expand each list:
Anonymous Cipher Suites – These cipher suites lack authentication, allowing attackers to impersonate servers, making them highly vulnerable to man-in-the-middle (MITM) attacks.
- TLS_DH_Anon_WITH_3DES_EDE_CBC_SHA
- TLS_DH_Anon_WITH_AES_128_CBC_SHA
- TLS_DH_Anon_WITH_AES_256_CBC_SHA
- TLS_ECDH_Anon_WITH_AES_128_CBC_SHA
- TLS_ECDH_Anon_WITH_AES_256_CBC_SHA
- TLS_ECDH_Anon_WITH_3DES_EDE_CBC_SHA
- TLS_ECDH_Anon_WITH_RC4_128_SHA
- TLS_ECDH_Anon_WITH_NULL_SHA
- TLS_DH_Anon_WITH_CAMELLIA_128_CBC_SHA
- TLS_DH_Anon_WITH_CAMELLIA_256_CBC_SHA
- TLS_DH_Anon_WITH_SEED_CBC_SHA
- TLS_DH_Anon_WITH_ARIA_128_CBC_SHA
- TLS_DH_Anon_WITH_ARIA_256_CBC_SHA
These suites are considered insecure and should be disabled in modern environments.
Null Cipher Suites – These cipher suites do not provide encryption, rendering the communication vulnerable to eavesdropping.
- TLS_NULL_WITH_NULL_NULL
- TLS_RSA_WITH_NULL_MD5
- TLS_RSA_WITH_NULL_SHA
- TLS_RSA_WITH_NULL_SHA256
- TLS_DHE_RSA_WITH_NULL_SHA
- TLS_DHE_RSA_WITH_NULL_SHA256
- TLS_DHE_RSA_WITH_NULL_MD5
- TLS_DHE_DSS_WITH_NULL_SHA
- TLS_DHE_DSS_WITH_NULL_SHA256
- TLS_DHE_DSS_WITH_NULL_MD5
- TLS_DH_RSA_WITH_NULL_SHA
- TLS_DH_RSA_WITH_NULL_SHA256
- TLS_DH_RSA_WITH_NULL_MD5
- TLS_DH_DSS_WITH_NULL_SHA
- TLS_DH_DSS_WITH_NULL_SHA256
- TLS_DH_DSS_WITH_NULL_MD5
- TLS_ECDHE_RSA_WITH_NULL_SHA
- TLS_ECDHE_RSA_WITH_NULL_SHA256
- TLS_ECDHE_RSA_WITH_NULL_SHA384
- TLS_ECDHE_RSA_WITH_NULL_MD5
- TLS_ECDHE_ECDSA_WITH_NULL_SHA
- TLS_ECDHE_ECDSA_WITH_NULL_SHA256
- TLS_ECDHE_ECDSA_WITH_NULL_SHA384
- TLS_ECDHE_ECDSA_WITH_NULL_MD5
- TLS_ECDH_RSA_WITH_NULL_SHA
- TLS_ECDH_RSA_WITH_NULL_SHA256
- TLS_ECDH_RSA_WITH_NULL_SHA384
- TLS_ECDH_RSA_WITH_NULL_MD5
- TLS_ECDH_ECDSA_WITH_NULL_SHA
- TLS_ECDH_ECDSA_WITH_NULL_SHA256
- TLS_ECDH_ECDSA_WITH_NULL_SHA384
- TLS_ECDH_ECDSA_WITH_NULL_MD5
- TLS_RSA_WITH_NULL_SHA
- TLS_RSA_WITH_NULL_SHA256
- TLS_RSA_WITH_NULL_SHA384
- TLS_RSA_WITH_NULL_MD5
- TLS_RSA_WITH_NULL_SHA1
- TLS_RSA_WITH_NULL_SHA224
- TLS_RSA_WITH_NULL_SHA256
- TLS_RSA_WITH_NULL_SHA384
- TLS_RSA_WITH_NULL_SHA512
- These cipher suites should be avoided as they do not provide any encryption.
Export-Grade Cipher Suites – These cipher suites were designed to comply with outdated U.S. export regulations limiting key strength to 40 or 56 bits. They are now considered insecure and should be disabled.
- TLS_RSA_EXPORT_WITH_RC4_40_MD5
- TLS_RSA_EXPORT_WITH_RC4_40_SHA
- TLS_RSA_EXPORT_WITH_DES40_CBC_SHA
- TLS_RSA_EXPORT_WITH_RC2_40_MD5
- TLS_RSA_EXPORT_WITH_RC2_40_SHA
- TLS_RSA_EXPORT_WITH_RC4_56_MD5
- TLS_RSA_EXPORT_WITH_RC4_56_SHA
- TLS_RSA_EXPORT_WITH_RC2_56_MD5
- TLS_RSA_EXPORT_WITH_RC2_56_SHA
RC4-Based Cipher Suites – RC4 has severe biases that allow plaintext recovery in some scenarios. RFC 7465 prohibits RC4 in TLS. All major browsers and OSes have dropped support.
Examples:
- TLS_RSA_WITH_RC4_128_MD5
- TLS_RSA_WITH_RC4_128_SHA
- TLS_ECDHE_RSA_WITH_RC4_128_SHA
- TLS_ECDHE_ECDSA_WITH_RC4_128_SHA
Block Ciphers with Small Block Sizes (3DES / DES) – 3DES uses a 64-bit block size which makes it vulnerable to Sweet32 birthday attacks. Single DES (like TLS_RSA_WITH_DES_CBC_SHA) is completely broken and should be avoided under all circumstances.
Examples:
- TLS_RSA_WITH_3DES_EDE_CBC_SHA
- TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA
- TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA
Static Key Exchanges (No Forward Secrecy) – If the private key is compromised, past communications can be decrypted. Use Ephemeral DH/ECDH (e.g., ECDHE) suites for Forward Secrecy.
Examples (non-Ephemeral RSA/DH):
- TLS_RSA_WITH_AES_128_CBC_SHA
- TLS_RSA_WITH_AES_256_CBC_SHA
- TLS_RSA_WITH_AES_128_GCM_SHA256
CBC Mode Ciphers in TLS < 1.2 – Susceptible to BEAST, Lucky13, and padding oracle attacks. CBC is more secure in TLS 1.2+, but TLS 1.3 removed CBC mode entirely.
Examples:
- TLS_RSA_WITH_AES_128_CBC_SHA
- TLS_DHE_RSA_WITH_AES_256_CBC_SHA
- TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
MD5-Based Cipher Suites – MD5 is broken — it is vulnerable to collision attacks.
Examples:
- TLS_RSA_WITH_AES_128_CBC_MD5
- TLS_RSA_WITH_RC4_128_MD5
- TLS_RSA_WITH_NULL_MD5
Cipher Suites Deprecated in TLS 1.3 – TLS 1.3 removed many older cipher suite types, including:
Examples:
- All CBC mode suites
- All RSA key exchange suites
- All non-AEAD suites (e.g., SHA-only or HMAC-based)
- All RC4, 3DES, DES, MD5, and NULL/EXPORT/ANON cipher suites
Certificate-Related Vulnerabilities – Problems with certificates can break the entire trust model of TLS.
| Issue | Description |
| Expired Certificates | Makes the connection insecure or unusable. |
| Self-Signed Certs | Not trusted by browsers or users. |
| Mismatched Hostnames | Cert doesn’t match domain name = browser warning. |
| Improper Validation | Missing or weak certificate validation (e.g., in IoT devices). |
🛠️ Mitigation: Use certs from trusted CAs, rotate before expiration, validate properly. Automate renewals and installs with Autoinstall SSL.
Implementation Vulnerabilities – These are flaws in how TLS libraries are coded — not in the protocol itself.
| Vulnerability | Affected Libraries |
| Heartbleed | OpenSSL — allowed memory leakage of private keys and data. |
| Lucky13 | Timing side-channel attack on CBC-mode ciphers. |
| DROWN | Cross-protocol flaw when SSLv2 is supported on same server. |
| FREAK / Logjam | Downgrade attacks due to support for weak RSA or DH. |
🛠️ Mitigation: Keep TLS libraries (e.g., OpenSSL, BoringSSL) up to date. Disable weak options.
Configuration & Operational Vulnerabilities – Even with strong protocols and ciphers, poor setup can expose your systems.
| Mistake | Risk |
| Not forcing HTTPS | Allows downgrade or MITM attacks. |
| No HSTS | Enables SSL stripping. |
| Open ports for SSLv2/v3 | Attackers can probe and exploit legacy services. |
| Weak DH parameters | Easier to break key exchange. |
🛠️ Mitigation: Use security scanners (e.g., Vulnerability Scanner), enforce HTTPS, enable HSTS, close unused ports.
Client-Side Vulnerabilities – Older Browsers, poor app validation, & dated iot devices are often a source of vulnerability.
| Issue | Example |
| Old browsers | May still support SSL 3.0 or weak ciphers. |
| Mobile apps | Often don’t validate certs properly, making them prone to MITM. |
| IoT devices | Frequently ship with outdated or insecure TLS stacks. |
🛠️ Mitigation: Educate users, enforce minimum TLS on server, patch apps and devices.
Timeline of SSL/TLS Vulnerability Breaches
SSL/TLS Vulnerability Mitigation Expert Guides
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OpenSSL Heartbleed Attack: How to Fix the Vulnerability
The OpenSSL Heartbleed bug, also known as CVE-2014-0160, is one of the most serious security vulnerabilities that have been detected in the OpenSSL cryptographic library. This bug, found in 2014, allows an attacker to read sensitive data from server memory such as passwords, session cookies, and private keys. This gives…
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Patching the LUCKY 13 Vulnerability: Solutions for IIS & More
LUCKY13 is an SSL/TLS protocol vulnerability that uses weakness in CBC-mode cipher padding for attacks. This flaw makes it easy for attackers to perform side-channel attacks that decrypt secret information, including login details, credit cards, and session tokens. This post explains the LUCKY13 vulnerability, its effect on your server, and…
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SSL Vulnerability Management: Tools and Best Practices
Proper SSL Vulnerability Management is mostly about staying on top of the latest in technology and best practices but it’s also something that’s becoming increasingly important to monitor. That’s why there’s a growing number of tools and setups that can help handle the management workload and mitigate down-time. In this…
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What is the FREAK Vulnerability? How to Prevent SSL FREAK attacks
The FREAK (Factoring RSA Export Keys) vulnerability known as CVE-2015-0204, is a major SSL/TLS security problem. It lets attackers make systems use weak encryption keys, which means they can intercept and decrypt secure communications. This article gives you a deep look at the FREAK vulnerability, shows an example of a…
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TLS/SSL Logjam Attack Vulnerability fix & CVE-2015-4000 exploit explained
The Logjam attack exploits weak 512-bit Diffie-Hellman (DH) key exchanges in SSL/TLS encryption. Such a weakness allows attackers to downgrade encryption and intercept or alter sensitive data. Learn how you can protect your server from the Logjam attack and secure your online communication. What is the Logjam Attack? The Logjam…
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What is the Drown Attack? How to patch the CVE-2016-0800 exploit
The DROWN attack, which stands for Decrypting RSA with Obsolete and Weakened Encryption, is a critical flaw in the SSL/TLS protocols. It exploits a server that still supports an old SSLv2 protocol, meaning an attacker can decrypt encrypted communications. This SSL vulnerability, tracked under CVE-2016-0800, exposes sensitive information such as…
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What is SSL Poodle Attack & How to Fix SSL Poodle Vulnerability
POODLE, which stands for “Padding Oracle on Downgraded Legacy Encryption”, is a vulnerability in SSL 3.0; the designation given to this CVE is CVE-2014-3566. An attacker can utilize weaknesses in how SSL 3.0 encrypts data to achieve access to user data. Although SSL 3.0 is now mostly considered deprecated, many…
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What is Heartbleed Vulnerability and how to protect your site from Heartbleed Bug
Heartbleed is a security bug that was found in OpenSSL cryptographic library back in 2014. Also known as CVE-2014-0160, this bug makes it possible for an attacker to steal sensitive information like private keys, session cookies, and passwords by exploiting the Heartbeat extension in OpenSSL. Here we’ll discuss Heartbleed, how…
SSL/TLS Vulnerability Statistics
How many websites do you visit that pass verification but still use vulnerable and deprecated configurations? We took the top 100 websites (by traffic) and compared their SSL/TLS configurations to a random cross-section of sites across the web and compared the two. See how they stack up:
| SSL/TLS Best Practice | Top 100 websites | Random Cross-section |
|---|---|---|
| SSL V2 still enabled | 0% | 0.18% |
| SSL V3 still enabled | 1% | 1.58% |
| Has TLS 1 | 40% | 23% |
| Has TLS 1.1 | 41% | 25% |
| TLS 1.2 not enabled | 0% | 40% |
| TLS 1.3 not enabled | 14% | 39% |
| HSTS Not Offered | 45% | 83% |
| Missing http: redirect | 29% | 23% |
SSL/TLS Risks & Vulnerabilities Course
Directly from Digicert’s SSL/TLS Professional Certification Training course, here you can learn about the various risks associated with improper or deprecated configurations. Watch the course in the video below:
Video Contents:
- Expired/Misconfigured Certificates
- Self Signed & Vendor Certificates
- Attacks on SSL: Heartbleed, POODLE, etc.
- Phishing Attacks