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CVE-2026-48126— Algernon: Host header path traversal in --domain mode reads files and runs Lua from parent dir

Quick assessment

Affected
xyproto algernon
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

algernon是Alexander F. Rødseth个人开发者的一个 Web 服务器。 Algernon 1.17.8之前版本存在安全漏洞，该漏洞源于使用--domain时通过Host标头进行路径遍历，可能导致任意文件读取、目录列表和Lua执行。

CVSS 8.2 · High EPSS 0.34% · P26

Affected Version Matrix 1

VendorProduct Version RangeStatus
xyproto algernon < 1.17.8 affected
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I. Basic Information for CVE-2026-48126

Vulnerability Information
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Vulnerability Title
Algernon: Host header path traversal in --domain mode reads files and runs Lua from parent dir
Source: CVE Program / CVE List V5
Vulnerability Description
Algernon is a small self-contained pure-Go web server. Prior to 1.17.8, when algernon is started with --domain (or --letsencrypt, which silently turns on --domain at engine/flags.go:372), the request handler resolves the served directory by joining the configured --dir with the value of the client-supplied Host header. The join is performed by filepath.Join with no validation, so a Host: .. header walks one level above the document root. Subsequent file resolution then exposes everything in that parent directory — arbitrary file read, full directory listing, and, if any .lua file is present, server-side Lua execution. This vulnerability is fixed in 1.17.8.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
对路径名的限制不恰当(路径遍历)
Source: CVE Program / CVE List V5
Vulnerability Title
algernon 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
algernon是Alexander F. Rødseth个人开发者的一个 Web 服务器。 Algernon 1.17.8之前版本存在安全漏洞，该漏洞源于使用--domain时通过Host标头进行路径遍历，可能导致任意文件读取、目录列表和Lua执行。
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
xyproto algernon < 1.17.8 -

II. Public POCs for CVE-2026-48126

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 8479 chars
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POC zip download
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III. Intelligence Information for CVE-2026-48126

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Vendor Advisories for CVE-2026-48126 (1)

Same Patch Batch · xyproto · 2026-05-26 · 7 CVEs total

CVE-2026-45721 9.0 CRITICAL Algernon: handler.lua discovery walks parent directories above the server root
CVE-2026-45728 7.5 HIGH Algernon: Single-file mode unconditionally enables debug mode
CVE-2026-46430 4.3 MEDIUM Algernon: Auto-refresh SSE event server binds to all interfaces by default on Linux/macOS
CVE-2026-46431 4.3 MEDIUM Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *
CVE-2026-43981 Algernon: Race Condition in handle() shared LState
CVE-2026-43982 Algernon: Path traversal file write via savein()

IV. Related Vulnerabilities

Same product: algernon
Same vendor: xyproto
Same weakness: CWE-22

V. Comments for CVE-2026-48126

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