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CVE-2026-85124

HIGHCVSS 7.5/10EPSS 0.55%

Last modified

CVE-2026-85124 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. @fastify/http-proxy versions before 11.6.2 do not validate proxied HTTP request paths for backslash based dot-segments before forwarding them to the configured upstream. The plain HTTP request handler skips the destination validation that the WebSocket path performs, and the underlying reply-from library only rejects forward-slash traversal, so a request containing backslash dot-segments can escape the boundary set by the prefix and rewritePrefix options. EPSS estimates a 0.55% chance of exploitation in the next 30 days.

Description

@fastify/http-proxy versions before 11.6.2 do not validate proxied HTTP request paths for backslash based dot-segments before forwarding them to the configured upstream. The plain HTTP request handler skips the destination validation that the WebSocket path performs, and the underlying reply-from library only rejects forward-slash traversal, so a request containing backslash dot-segments can escape the boundary set by the prefix and rewritePrefix options. An unauthenticated network attacker can use this to reach upstream paths that were meant to stay hidden behind the proxy, resulting in disclosure of internal endpoints. This is a path traversal issue (CWE-22). Users should upgrade to @fastify/http-proxy 11.6.2 or later.

Metrics

CVSS 3.1
7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS Probability
0.55%

44.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
FastifyFastify\/Http-Proxy< 11.6.2

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is CVE-2026-85124?
@fastify/http-proxy versions before 11.6.2 do not validate proxied HTTP request paths for backslash based dot-segments before forwarding them to the configured upstream. The plain HTTP request handler skips the destination validation that the WebSocket path performs, and the underlying reply-from library only rejects forward-slash traversal, so a request containing backslash dot-segments can escape the boundary set by the prefix and rewritePrefix options. An unauthenticated network attacker can use this to reach upstream paths that were meant to stay hidden behind the proxy, resulting in disclosure of internal endpoints. This is a path traversal issue (CWE-22). Users should upgrade to @fastify/http-proxy 11.6.2 or later.
How severe is CVE-2026-85124?
CVE-2026-85124 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.55% probability of exploitation in the next 30 days.
How do I fix CVE-2026-85124?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST