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CVE-2021-32656— Trusted servers exchange can be triggered by attacker

Quick assessment

Affected
nextcloud security-advisories
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Nextcloud是德国Nextcloud公司的一套开源的自托管文件同步和共享的通信应用平台。 Nextcloud Server存在安全漏洞，攻击者利用该漏洞可以通过访问合法服务器用户添加为联邦共享的公共链接来访问服务器用户的基本信息。以下产品和版本受到影响：Nextcloud Server 19.0.11、20.0.10或21.0.2之前的版本。

CVSS 8.6 · High EPSS 1.84% · P78

Possible ATT&CK Techniques 1 AI

T1530 · Data from Cloud Storage
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I. Basic Information for CVE-2021-32656

Vulnerability Information
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Vulnerability Title
Trusted servers exchange can be triggered by attacker
Source: CVE Program / CVE List V5
Vulnerability Description
Nextcloud Server is a Nextcloud package that handles data storage. A vulnerability in federated share exists in versions prior to 19.0.11, 20.0.10, and 21.0.2. An attacker can gain access to basic information about users of a server by accessing a public link that a legitimate server user added as a federated share. This happens because Nextcloud supports sharing registered users with other Nextcloud servers, which can be done automatically when selecting the "Add server automatically once a federated share was created successfully" setting. The vulnerability is patched in versions 19.0.11, 20.0.10, and 21.0.2 As a workaround, disable "Add server automatically once a federated share was created successfully" in the Nextcloud settings.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
访问控制不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Nextcloud 访问控制错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Nextcloud是德国Nextcloud公司的一套开源的自托管文件同步和共享的通信应用平台。 Nextcloud Server存在安全漏洞，攻击者利用该漏洞可以通过访问合法服务器用户添加为联邦共享的公共链接来访问服务器用户的基本信息。以下产品和版本受到影响：Nextcloud Server 19.0.11、20.0.10或21.0.2之前的版本。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
nextcloud security-advisories < 19.0.11 -

II. Public POCs for CVE-2021-32656

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III. Intelligence Information for CVE-2021-32656

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Vendor Advisories for CVE-2021-32656 (2)

Other References for CVE-2021-32656 (1)

Same Patch Batch · nextcloud · 2021-06-01 · 6 CVEs total

CVE-2021-32652 8.8 HIGH Missing permission check on email metadata retrieval
CVE-2021-32654 8.1 HIGH Attacker can obtain write access to any federated share/public link
CVE-2021-32657 4.3 MEDIUM Malicious user could break user administration page
CVE-2021-32655 3.5 LOW Files Drop public link can be added as federated share
CVE-2021-32653 2.7 LOW Default settings leak federated cloud ID to lookup server of all users

IV. Related Vulnerabilities

Same product: security-advisories
Same vendor: nextcloud
Same weakness: CWE-284

V. Comments for CVE-2021-32656

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