Question 97 of 978
hardMultiple ChoiceObjective-mapped
HTTPS Certificate Pinning in Cisco WSA Decryption
A company using Cisco Web Security Appliance (WSA) in explicit proxy mode has enabled HTTPS decryption with a custom CA certificate. A user reports that a specific banking website displays a certificate error message. The administrator verifies that the WSA is generating a certificate for that site. What is the most likely cause of the error?
Quick Answer
The answer is certificate pinning, specifically HTTP Public Key Pinning (HPKP), which causes the certificate error on the banking site. When Cisco WSA performs HTTPS decryption, it generates a new certificate on the fly signed by the company’s custom CA, but banking websites often embed a hash of their original public key or certificate into the browser’s security policy. If the WSA’s generated certificate does not match that pinned public key, the browser rejects the connection as untrusted, even though the CA is valid. On the Cisco SCOR 350-701 exam, this scenario tests your understanding of how HTTPS decryption interacts with modern security mechanisms like certificate pinning—a common trap is assuming the custom CA trust alone resolves all errors. Remember the mnemonic: “Pinning pins the public key, not the CA.”
⚠ Common exam trap
Cisco often tests the distinction between global certificate trust issues (e.g., untrusted CA) and site-specific pinning errors, where candidates mistakenly choose the browser trust option because they overlook that the error is isolated to one site.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The banking website uses HTTP Public Key Pinning (HPKP) or Certificate Pinning.
The most likely cause is that the banking website uses HTTP Public Key Pinning (HPKP) or certificate pinning. When the WSA performs HTTPS decryption, it generates a new certificate for the site, which does not match the pinned public key or certificate hash that the browser expects. This mismatch triggers a certificate error, even though the WSA's CA is trusted.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The banking website uses HTTP Public Key Pinning (HPKP) or Certificate Pinning.
Why this is correct
Pinned certificates are compared to the original, and the WSA's generated certificate does not match, causing an error.
- ✗
The WSA's time is not synchronized with the NTP server, causing certificate validity issues.
Why it's wrong here
Time sync issues would affect all HTTPS sites, not just this bank.
- ✗
The WSA is not configured to generate certificates for that domain.
Why it's wrong here
The administrator verified a certificate is generated.
- ✗
The user's browser does not trust the WSA's CA certificate.
Why it's wrong here
If the CA is trusted, no error would occur; the error is specific to the certificate presented.
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Same concept, more angles
2 more ways this is tested on 350-701
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company uses Cisco Web Security Appliance (WSA) in explicit proxy mode. Users report that some HTTPS websites fail to load. The administrator checks the logs and sees that the WSA is not generating any certificate for those sites. What is the most likely cause?
easy- ✓ A.HTTPS decryption is disabled globally or for the specific category.
- B.The website uses certificate pinning, which prevents interception.
- C.The WSA CA certificate is not installed in the user's browser trust store.
- D.The WSA is configured to bypass decryption for the user's subnet.
Why A: When HTTPS decryption is disabled globally or for a specific category, the WSA does not generate a certificate for those sites. If the proxy policy requires decryption for that category (a common security configuration), the connection is blocked, causing the websites to fail to load. The absence of a generated certificate in the logs directly indicates that decryption is not enabled for those sites.
Variation 2. A Cisco WSA appliance is configured with explicit proxy mode. Users report that they cannot access external HTTPS websites, but HTTP works fine. The proxy logs show 'SSL handshake failed' errors. What is the most likely reason?
hard- A.The HTTPS proxy port is not configured on the WSA.
- ✓ B.The WSA's SSL certificate is not trusted by the clients.
- C.The WSA is configured to forward HTTPS traffic without decryption.
- D.Client certificates are required for authentication.
Why B: In explicit proxy mode, the Cisco WSA must intercept HTTPS traffic by performing a man-in-the-middle (MITM) decryption. For this to work, the WSA presents its own SSL certificate to the client. If that certificate is not trusted by the client's browser or operating system (i.e., not installed in the trusted root certificate store), the client will reject the SSL handshake, resulting in 'SSL handshake failed' errors. HTTP traffic is unaffected because it does not involve certificate validation.
Last reviewed: Jul 4, 2026
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