CVE-2026-16158Network attack vector

Cross-upstream data access and modification via cache collision

Published Jul 18, 2026 · Updated Jul 18, 2026

Cache key collision in Fastify @fastify/reply-from 8.3.1 through 12.6.3 allows remote attackers to access or modify data across upstreams. The URL cache concatenates the selected destination and source path without a delimiter, causing distinct pairs to reuse a URL resolved for another upstream. The default cache is affected when request data can influence the source path or getUpstream selection, with no authentication or user interaction required.

CVSS severity8.7
High
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cache key collision in Fastify @fastify/reply-from 8.3.1 through 12.6.3 allows remote attackers to access or modify data across upstreams. The URL cache concatenates the selected destination and source path without a delimiter, causing distinct pairs to reuse a URL resolved for another upstream. The default cache is affected when request data can influence the source path or getUpstream selection, with no authentication or user interaction required.

The record

CVE
CVE-2026-16158
Published
Jul 18, 2026
Updated
Jul 18, 2026
Vendor
Fastify
Product
@fastify/reply-from
Classifications
CWE-441, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 18, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 18, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=8.3.1 <12.6.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Fastify · @fastify/reply-fromversion=8.3.1 <12.6.4

Published CVSS scores

8.7OpenJS FoundationCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N
10.0NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-441Unintended Proxy or Intermediary ('Confused Deputy')
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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