CVE-2020-8156Network attack vector

Mail interception via missing TLS hostname verification

Published May 12, 2020 · Updated Aug 4, 2024

Improper certificate validation in Nextcloud Mail 1.1.3 allows man-in-the-middle attackers to intercept TLS mail connections. The IMAP and SMTP connection setup accepts a TLS certificate whose hostname does not match the configured mail server. An attacker positioned on the network path can impersonate the mail server, exposing mail content and credentials and permitting message manipulation.

CVSS severity7.0
High
EPSS probability0.93%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate validation in Nextcloud Mail 1.1.3 allows man-in-the-middle attackers to intercept TLS mail connections. The IMAP and SMTP connection setup accepts a TLS certificate whose hostname does not match the configured mail server. An attacker positioned on the network path can impersonate the mail server, exposing mail content and credentials and permitting message manipulation.

The record

CVE
CVE-2020-8156
Published
May 12, 2020
Updated
Aug 4, 2024
Vendor
Nextcloud GmbH
Product
Nextcloud Mail
Classifications
CWE-295, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 12, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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=1.1.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Nextcloud GmbH · Nextcloud Mailversion=1.1.4

Published CVSS scores

6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
7.0NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:L

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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-295Improper Certificate Validation
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

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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