WebDAV sync fails with SEC_ERROR_UNKNOWN_ISSUER on Zotero 9.0.4 for macOS, but works in browsers and

IceCream314
Hello,

I am having a WebDAV sync problem with Zotero 9.0.4 on macOS 26.5.

My WebDAV server is hosted on a QNAP NAS using a QNAP DDNS domain, and the SSL certificate is a Let’s Encrypt certificate. The same WebDAV URL can be opened normally in multiple browsers without any SSL/security warning. I can also browse the WebDAV directory from the web interface without any certificate warning.

More importantly, Zotero for iPad can use the same WebDAV server successfully without any SSL certificate problem.

However, on desktop Zotero 9.0.4 for macOS, WebDAV verification/sync fails with:

SEC_ERROR_UNKNOWN_ISSUER

This happens on multiple desktop devices and in different networks, including both my office and home networks. So it does not seem to be limited to one computer, one local network, or one browser certificate cache. At the moment, only Zotero for iPad works normally.

Because the WebDAV URL works in browsers and Zotero for iPad, I suspect this may be related to how Zotero desktop handles the certificate or certificate chain.

Could this be a certificate handling issue in Zotero 9.0.4 for macOS? Is there any way to check which certificate chain Zotero desktop is seeing, or to force Zotero desktop to refresh/rebuild its certificate store?

Thank you.
  • dstillman Zotero Team
    edited 4 hours ago
    I'd guess that your server isn't correctly sending an intermediate certificate. Zotero, like Firefox (which it's based on), won't download an intermediate certificate. (You'd likely see the same thing in a new Firefox profile. It could work in an existing profile if another site served the same intermediate certificate.)

    https://www.zotero.org/support/kb/incomplete_cert_chain
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