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CVE-2026-117518— @fastify/reply-from vulnerable to path traversal via backslash dot-segment prefix escape

Quick assessment

Affected
@fastify/reply-from @fastify/reply-from
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.

是一个 Fastify 插件，用于将请求转发到上游 HTTP 服务器。在 12.8.0 及更早版本中，该插件仅针对正斜杠点段（forward-slash dot-segments）对代理路径进行验证，随后使用 WHATWG URL 解析器构建目标地址。该解析器会对 、 、 和 方案中的反斜杠及其百分号编码形式进行规范化，将其转换为正斜杠。因此，使用反斜杠点段的路径能够绕过遍历检查，解析为不同的上游路径。这导致原本限制代理范围于特定上游前缀、或依赖转发调用前的路由守卫的应用，可能使未认证请求逃逸出预期前缀，访问其他上

CVSS 8.2 · High
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I. Basic Information for CVE-2026-117518

Vulnerability Information
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Vulnerability Title
@fastify/reply-from vulnerable to path traversal via backslash dot-segment prefix escape
Source: CVE Program / CVE List V5
Vulnerability Description
@fastify/reply-from is a Fastify plugin that forwards requests to an upstream HTTP server. In versions up to and including 12.8.0, the plugin validated proxy paths against forward-slash dot-segments only and then built the target with the WHATWG URL parser, which normalizes a backslash and its percent-encoded form to a forward slash on the http, https, ws, and wss schemes. A path that uses backslash dot-segments therefore bypasses the traversal check and resolves to a different upstream path, so an application that scopes proxying to an upstream prefix, or relies on route guards in front of the forwarding call, can have an unauthenticated request escape the intended prefix and reach other upstream endpoints. The resulting access to unintended upstream resources is primarily a confidentiality impact with limited integrity impact. The issue is fixed in @fastify/reply-from 12.8.1, where the path is normalized and any segment resolving to a single or double dot, along with control characters and ambiguous whitespace, is rejected before the URL is constructed, and users should upgrade to 12.8.1 or later. There is no workaround other than upgrading.
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

Affected Products

Vendor Product Affected Versions CPE Subscribe
@fastify/reply-from @fastify/reply-from 0 ~ 12.8.1 -

II. Public POCs for CVE-2026-117518

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III. Intelligence Information for CVE-2026-117518

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Vendor Advisories for CVE-2026-117518 (1)

IV. Related Vulnerabilities

Same product: @fastify/reply-from
Same vendor: @fastify/reply-from
Same weakness: CWE-22