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CVE-2026-23963— Mastodon missing length limits on list names, filter names, and filter keywords

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开源的一款基于ActivityPub的开源社交网络服务器。 Mastodon v4.5.5之前版本、v4.4.12之前版本和v4.3.18之前版本存在安全漏洞，该漏洞源于未强制实施列表、过滤器名称或过滤器关键词的最大长度，可能导致资源滥用。

CVSS 4.3 · Medium EPSS 0.34% · P26

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking
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I. Basic Information for CVE-2026-23963

Vulnerability Information
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Vulnerability Title
Mastodon missing length limits on list names, filter names, and filter keywords
Source: CVE Program / CVE List V5
Vulnerability Description
Mastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.5.5, 4.4.12, and 4.3.18, the server does not enforce a maximum length for the names of lists or filters, or for filter keywords, allowing any user to set an arbitrarily long string as the name or keyword. Any local user can abuse the list or filter fields to cause disproportionate storage and computing resource usage. They can additionally cause their own web interface to be unusable, although they must intentionally do this to themselves or unknowingly approve a malicious API client. Mastodon versions v4.5.5, v4.4.12, v4.3.18 are patched.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
不加限制或调节的资源分配
Source: CVE Program / CVE List V5
Vulnerability Title
Mastodon 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mastodon是Mastodon开源的一款基于ActivityPub的开源社交网络服务器。 Mastodon v4.5.5之前版本、v4.4.12之前版本和v4.3.18之前版本存在安全漏洞，该漏洞源于未强制实施列表、过滤器名称或过滤器关键词的最大长度，可能导致资源滥用。
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 < 4.3.18 -

II. Public POCs for CVE-2026-23963

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III. Intelligence Information for CVE-2026-23963

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Same Patch Batch · mastodon · 2026-01-22 · 4 CVEs total

CVE-2026-23962 7.5 HIGH Mastodon vulnerable to Denial of Service from a single post (client/server)
CVE-2026-23964 6.5 MEDIUM Mastodon has insufficient access control to push notification settings
CVE-2026-23961 5.3 MEDIUM Mastodon may allow a remote suspension bypass

IV. Related Vulnerabilities

Same product: mastodon
Same vendor: mastodon
Same weakness: CWE-770

V. Comments for CVE-2026-23963

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