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CVE-2021-43802— Admin privilege escalation and arbitrary code execution via malicious *.etherpad imports

Quick assessment

Affected
ether etherpad-lite
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.

Etherpad是开源的一个基于Web的在线文档协作工具。多个用户可以通过Etherpad同时编写一个文本文档，并看到所有的参与者的实时编辑。 Etherpad 1.8.16之前版本存在安全漏洞，该漏洞源于软件对于etherpad文件处理存在问题，攻击者可以制作“*.etherpad”文件，导入该文件后，攻击者可能会获得 Etherpad 实例的管理员权限。

CVSS 9.9 · Critical EPSS 2.06% · P81
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I. Basic Information for CVE-2021-43802

Vulnerability Information
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Vulnerability Title
Admin privilege escalation and arbitrary code execution via malicious *.etherpad imports
Source: CVE Program / CVE List V5
Vulnerability Description
Etherpad is a real-time collaborative editor. In versions prior to 1.8.16, an attacker can craft an `*.etherpad` file that, when imported, might allow the attacker to gain admin privileges for the Etherpad instance. This, in turn, can be used to install a malicious Etherpad plugin that can execute arbitrary code (including system commands). To gain privileges, the attacker must be able to trigger deletion of `express-session` state or wait for old `express-session` state to be cleaned up. Core Etherpad does not delete any `express-session` state, so the only known attacks require either a plugin that can delete session state or a custom cleanup process (such as a cron job that deletes old `sessionstorage:*` records). The problem has been fixed in version 1.8.16. If users cannot upgrade to 1.8.16 or install patches manually, several workarounds are available. Users may configure their reverse proxies to reject requests to `/p/*/import`, which will block all imports, not just `*.etherpad` imports; limit all users to read-only access; and/or prevent the reuse of `express_sid` cookie values that refer to deleted express-session state. More detailed information and general mitigation strategies may be found in the GitHub Security Advisory.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
特殊元素过滤不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Etherpad 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Etherpad是开源的一个基于Web的在线文档协作工具。多个用户可以通过Etherpad同时编写一个文本文档，并看到所有的参与者的实时编辑。 Etherpad 1.8.16之前版本存在安全漏洞，该漏洞源于软件对于etherpad文件处理存在问题，攻击者可以制作“*.etherpad”文件，导入该文件后，攻击者可能会获得 Etherpad 实例的管理员权限。
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
ether etherpad-lite < 1.8.16 -

II. Public POCs for CVE-2021-43802

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III. Intelligence Information for CVE-2021-43802

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Vendor Advisories for CVE-2021-43802 (1)

Other References for CVE-2021-43802 (3)

IV. Related Vulnerabilities

Same vendor: ether
Same weakness: CWE-790

V. Comments for CVE-2021-43802

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