What’s Vulnerable › Vulnerabilities

CVE-2021-39220: Bypass of image blocking in Nextcloud Mail

• Severity: low (CVSS 3.5 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-10-25 · updated 2026-06-17
• Weakness: CWE-20

Description

Nextcloud is an open-source, self-hosted productivity platform The Nextcloud Mail application prior to versions 1.10.4 and 1.11.0 does by default not render images in emails to not leak the read state or user IP. The privacy filter failed to filter images with a relative protocol. It is recommended that the Nextcloud Mail application is upgraded to 1.10.4 or 1.11.0. There are no known workarounds aside from upgrading.

Affected products

• nextcloud Mail: before 1.10.4 — fixed in 1.10.4

How to fix

Upgrade to a fixed version: nextcloud Mail 1.10.4. Check the vendor advisory for mitigations.

References

• https://github.com/nextcloud/mail/pull/5470
• https://github.com/nextcloud/security-advisories/security/advisories/GHSA-6q9v-wm8r-rcv5
• https://hackerone.com/reports/1308147
• https://github.com/nextcloud/mail/pull/5470
• https://github.com/nextcloud/security-advisories/security/advisories/GHSA-6q9v-wm8r-rcv5
• https://hackerone.com/reports/1308147

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