CVE-2021-32707Public exploitNetwork attack vector

Read-state disclosure via unsanitized CSS image URLs

Published Jul 12, 2021 · Updated Aug 3, 2024

Information disclosure in Nextcloud Mail before 1.9.6 allows remote authenticated users to reveal message-read state via crafted email CSS. The HTML message sanitizer leaves URL values in style sheets and CSS style attributes, allowing background images to load through the image proxy. A recipient must open the crafted message while external images remain blocked; the proxy prevents recipient IP disclosure, but its request signals that the message was read.

CVSS severity4.3
Medium
EPSS probability1.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Nextcloud Mail before 1.9.6 allows remote authenticated users to reveal message-read state via crafted email CSS. The HTML message sanitizer leaves URL values in style sheets and CSS style attributes, allowing background images to load through the image proxy. A recipient must open the crafted message while external images remain blocked; the proxy prevents recipient IP disclosure, but its request signals that the message was read.

The record

CVE
CVE-2021-32707
Published
Jul 12, 2021
Updated
Aug 3, 2024
Vendor
Nextcloud GmbH
Product
Nextcloud Security Advisories
Classifications
CWE-200, CWE-20
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 12, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.9.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Nextcloud GmbH · Nextcloud Security Advisoriesversion=< 1.9.6

Published CVSS scores

4.3GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
4.0NIST NVDAV:N/AC:L/Au:S/C:N/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-200Exposure of Sensitive Information to an Unauthorized Actor
CWE-20Improper Input Validation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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