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CVE-2025-24356— UDP traffic amplification via fastd's fast reconnect feature

Quick assessment

Affected
neocturne fastd
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.

fastd是中国Fastdlabs团队的一个支持 Swoole 的轻量级 Web 开发框架。 fastd 23之前版本存在安全漏洞，该漏洞源于存在UDP流量放大漏洞，从而导致分布式拒绝服务攻击。

AI Predicted 5.3 Difficulty: Easy EPSS 0.67% · P49
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I. Basic Information for CVE-2025-24356

Vulnerability Information
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Vulnerability Title
UDP traffic amplification via fastd's fast reconnect feature
Source: CVE Program / CVE List V5
Vulnerability Description
fastd is a VPN daemon which tunnels IP packets and Ethernet frames over UDP. When receiving a data packet from an unknown IP address/port combination, fastd will assume that one of its connected peers has moved to a new address and initiate a reconnect by sending a handshake packet. This "fast reconnect" avoids having to wait for a session timeout (up to ~90s) until a new connection is established. Even a 1-byte UDP packet just containing the fastd packet type header can trigger a much larger handshake packet (~150 bytes of UDP payload). Including IPv4 and UDP headers, the resulting amplification factor is roughly 12-13. By sending data packets with a spoofed source address to fastd instances reachable on the internet, this amplification of UDP traffic might be used to facilitate a Distributed Denial of Service attack. This vulnerability is fixed in v23.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:N/SA:L
Source: CVE Program / CVE List V5
Vulnerability Type
不对称的资源消耗(放大攻击)
Source: CVE Program / CVE List V5
Vulnerability Title
fastd 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
fastd是中国Fastdlabs团队的一个支持 Swoole 的轻量级 Web 开发框架。 fastd 23之前版本存在安全漏洞，该漏洞源于存在UDP流量放大漏洞，从而导致分布式拒绝服务攻击。
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
neocturne fastd < 23 -

II. Public POCs for CVE-2025-24356

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III. Intelligence Information for CVE-2025-24356

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IV. Related Vulnerabilities

Same weakness: CWE-405

V. Comments for CVE-2025-24356

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