What’s Vulnerable › Vulnerabilities

CVE-2021-32707: Bypass of image blocking in Nextcloud Mail

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.1% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-07-12 · updated 2026-06-17
• Weakness: CWE-20

Description

Nextcloud Mail is a mail app for Nextcloud. In versions prior to 1.9.6, the Nextcloud Mail application does not, by default, render images in emails to not leak the read state. The privacy filter failed to filter images with a `background-image` CSS attribute. Note that the images were still passed through the Nextcloud image proxy, and thus there was no IP leakage. The issue was patched in version 1.9.6 and 1.10.0. No workarounds are known to exist.

Affected products

• nextcloud Mail: before 1.9.6 — fixed in 1.9.6

How to fix

Upgrade to a fixed version: nextcloud Mail 1.9.6. Check the vendor advisory for mitigations.

References

• https://github.com/nextcloud/mail/pull/5189
• https://github.com/nextcloud/security-advisories/security/advisories/GHSA-xxp4-44xc-8crh
• https://hackerone.com/reports/1215251
• https://github.com/nextcloud/mail/pull/5189
• https://github.com/nextcloud/security-advisories/security/advisories/GHSA-xxp4-44xc-8crh
• https://hackerone.com/reports/1215251

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