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CVE-2026-72916— Mastodon: SSRF Protection Bypass via IPv4-compatible IPv6 Addresses

Quick assessment

Affected
mastodon mastodon
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.

Mastodon是Mastodon组织的一款去中心化社交网络服务器软件。 Mastodon 4.4.21之前版本、4.5.14之前版本、4.6.4之前版本和4.7.0-beta.1之前版本存在安全漏洞，该漏洞源于PrivateAddressCheck.private_address?方法未识别IPv4兼容IPv6地址，导致攻击者绕过ALLOWED_PRIVATE_ADDRESSES保护，使Mastodon发送HTTP请求到回环接口，可能访问私有资源和服务。

CVSS 6.3 · Medium EPSS 0.59% · P46

Affected Version Matrix 3

VendorProduct Version RangeStatus
mastodon mastodon < 4.4.21 affected
>= 4.5.0-beta.1, < 4.5.14 affected
>= 4.6.0-beta.1, < 4.6.4 affected
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I. Basic Information for CVE-2026-72916

Vulnerability Information
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Vulnerability Title
Mastodon: SSRF Protection Bypass via IPv4-compatible IPv6 Addresses
Source: CVE Program / CVE List V5
Vulnerability Description
Mastodon is a free, open-source social network server based on ActivityPub. Prior to 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1, PrivateAddressCheck.private_address? in app/lib/private_address_check.rb normalized IPv4-mapped IPv6 addresses but did not recognize IPv4-compatible IPv6 addresses with IPAddr#ipv4_compat?. An attacker could supply an address in the omitted range to bypass the ALLOWED_PRIVATE_ADDRESSES protection and make Mastodon send HTTP requests to loopback interfaces, potentially accessing private resources and services. Exploitation requires a system that supports the obsolete IPv4-compatible IPv6 mechanism. This issue is fixed in versions 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:L
Source: CVE Program / CVE List V5
Vulnerability Type
服务端请求伪造(SSRF)
Source: CVE Program / CVE List V5
Vulnerability Title
Mastodon 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mastodon是Mastodon组织的一款去中心化社交网络服务器软件。 Mastodon 4.4.21之前版本、4.5.14之前版本、4.6.4之前版本和4.7.0-beta.1之前版本存在安全漏洞，该漏洞源于PrivateAddressCheck.private_address?方法未识别IPv4兼容IPv6地址，导致攻击者绕过ALLOWED_PRIVATE_ADDRESSES保护，使Mastodon发送HTTP请求到回环接口，可能访问私有资源和服务。
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
mastodon mastodon < 4.4.21 -

II. Public POCs for CVE-2026-72916

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III. Intelligence Information for CVE-2026-72916

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Patches & Fixes for CVE-2026-72916 (4)

Vendor Advisories for CVE-2026-72916 (1)

Vendor Pages for CVE-2026-72916 (3)

Same Patch Batch · mastodon · 2026-08-10 · 3 CVEs total

CVE-2026-72915 7.5 HIGH Mastodon: Personally-identifying information disclosure due to incorrect access control va
CVE-2026-72914 7.5 HIGH Mastodon: Exhausting data by an unauthenticated request to the admin retention API

IV. Related Vulnerabilities

Same product: mastodon
Same vendor: mastodon
Same weakness: CWE-918

V. Comments for CVE-2026-72916

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