CVE-2021-26560Network attack vector

Server spoofing via cleartext HTTP session

Published Feb 26, 2021 · Updated Sep 17, 2024

Cleartext transmission in Synology DiskStation Manager before 6.2.3-25426-3 allows man-in-the-middle attackers to spoof servers via HTTP. The synoagentregisterd service sends its server-finder requests over plaintext HTTP and accepts an attacker-modified syno_finder_site response, enabling redirection to an impostor server. A network-positioned attacker must intercept the session; spoofing can redirect registration traffic and, in the related unsafe memory handling path, lead to code execution, while this CVE's stated impact is server spoofing.

CVSS severity9.0
Critical
EPSS probability0.75%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cleartext transmission in Synology DiskStation Manager before 6.2.3-25426-3 allows man-in-the-middle attackers to spoof servers via HTTP. The synoagentregisterd service sends its server-finder requests over plaintext HTTP and accepts an attacker-modified syno_finder_site response, enabling redirection to an impostor server. A network-positioned attacker must intercept the session; spoofing can redirect registration traffic and, in the related unsafe memory handling path, lead to code execution, while this CVE's stated impact is server spoofing.

The record

CVE
CVE-2021-26560
Published
Feb 26, 2021
Updated
Sep 17, 2024
Vendor
Synology
Product
Synology DiskStation Manager
Classifications
CWE-319, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 26, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 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=unspecified <6.2.3-25426-3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Synology · Synology DiskStation Managerversion=unspecified <6.2.3-25426-3

Published CVSS scores

9.0SynologyCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

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-319Cleartext Transmission of Sensitive Information
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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