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CVE-2021-32655— Files Drop public link can be added as federated share

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，该漏洞源于当共享用户打开共享面板并试图删除此意外共享的“Create”特权时，Nextcloud服务器将静默地授予该共享读取特权。攻击者可利用该漏洞将Files Drop链接转换为联邦共享，这将导致共享用户的UI端出现问题。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 3.5 · Low EPSS 1.03% · P63

Possible ATT&CK Techniques 1 AI

T1528 · Steal Application Access Token
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I. Basic Information for CVE-2021-32655

Vulnerability Information
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Vulnerability Title
Files Drop public link can be added as federated share
Source: CVE Program / CVE List V5
Vulnerability Description
Nextcloud Server is a Nextcloud package that handles data storage. In versions prior to 19.0.11, 20.0.10, and 21.0.2, an attacker is able to convert a Files Drop link to a federated share. This causes an issue on the UI side of the sharing user. When the sharing user opens the sharing panel and tries to remove the "Create" privileges of this unexpected share, Nextcloud server would silently grant the share read privileges. The vulnerability is patched in versions 19.0.11, 20.0.10 and 21.0.2. No workarounds are known to exist.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
非预期数据类型处理不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Nextcloud 安全漏洞
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，该漏洞源于当共享用户打开共享面板并试图删除此意外共享的“Create”特权时，Nextcloud服务器将静默地授予该共享读取特权。攻击者可利用该漏洞将Files Drop链接转换为联邦共享，这将导致共享用户的UI端出现问题。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-2021-32655

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III. Intelligence Information for CVE-2021-32655

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Vendor Advisories for CVE-2021-32655 (2)

Other References for CVE-2021-32655 (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-2021-32656 8.6 HIGH Trusted servers exchange can be triggered by attacker
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-2021-32653 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-241

V. Comments for CVE-2021-32655

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