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Vulnerabilities/CVE-2026-33805Public Intelligence Dossier
Source: fastify · Limited verification•Last verified: •Collection Degraded
CVE-2026-33805Unknown / EvaluatingCRITICAL (raw)CVSS 9.0CWE-644

@fastify/reply-from v12.6.1 and earlier and @fastify/http-proxy v11.4.3 and earlier process the client's Connection header after the proxy has added its own headers via rewriteRequestHeaders

Published: 15 Apr 2026•Last updated: 27 Oct 2026, 03:40 AM IST•Source identifier: ce714d77-add3-4f53-aff5-83d477b104bb
Dossier completeness: source-provided sections 2 / 3 · rule guidance available. Missing source facts count as incomplete.
Official source
CISA KEV catalog
Unknown
KEV status was not determined.
CVSS score
9.0CRITICAL (raw)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Metric sourcece714d77-add3-4f53-aff5-83d477b104bb
EPSS probability
0.4%0.004
Percentile38th
Weakness type
CWE-644
CWE-444
Remediation
Patch status unknown
No fixed version or KB recorded

Why It Matters

Analysis dossier

Why It Matters

@fastify/reply-from v12.6.1 and earlier and @fastify/http-proxy v11.4.3 and earlier process the client's Connection header after the proxy has added its own headers via rewriteRequestHeaders. This allows attackers to retroactively strip proxy-added headers from upstream requests by listing them in the Connection header value. Any header added by the proxy for routing, access control, or security purposes can be selectively removed by a client. @fastify/http-proxy is also affected as it delegates to @fastify/reply-from. Upgrade to @fastify/reply-from v12.6.2 or @fastify/http-proxy v11.4.4 or later.

SOC priority

High Severity / Review

Actively exploited (source statement)

Unknown

Publicly disclosed

Unknown

Risk basis: SOC ecosystem technology relevance; CRITICAL severity; Critical source severity without confirmed exploitation

Affected Products & Remediation

2 source-backed products
Affected products and versions (source)
  • fastify fastify\/http-proxy · < 11.4.4 · NVD CPE · Source
  • fastify reply-from · < 12.6.2 · NVD CPE · Source
Recorded patch / KBNot provided by source

Vendor or catalog guidance (source)

Not provided by source

Known exploitation (source facts)

Only what a source states. Unknown means no source has said either way; it is not "not exploited".

CISA KEV
Unknown
Exploited (source statement)
Unknown
Publicly disclosed (source)
Unknown

Suggested hunting (rule-based inference)

SecOps Signal recommendation (rule-based inference). These steps are hunting hypotheses from the vulnerability class; they do not state or imply that exploitation occurred here or anywhere.

Matched network-unauthenticated (CVSS AV:N, CVSS PR:N, CVSS UI:N)

Exposure

  1. Identify devices reporting this CVE and note which expose the affected service to untrusted networks.Telemetry: DeviceTvmSoftwareVulnerabilities · A network-reachable, no-privilege vector makes internet-facing instances the first exposure question. · Rule network-unauthenticated

Exploitation evidence

  1. Review inbound connections to the affected service from unexpected sources since the advisory date.Telemetry: DeviceNetworkEvents · Hunting hypothesis from the CVSS vector; it does not show that exploitation occurred. · Rule network-unauthenticated

Response

  1. Confirm the source-stated update is installed and the CVE is no longer reported.Telemetry: DeviceTvmSoftwareVulnerabilities · A follow-up inventory check verifies remediation. · Rule network-unauthenticated

CISA KEV Record

CISA KEV status was not determined for this record.

Change History & Source Data

— No recorded material change

CNA / source
ce714d77-add3-4f53-aff5-83d477b104bb
Record status · verification
UPDATED · NVD API
CPE
cpe:2.3:a:fastify:fastify\/http-proxy:*:*:*:*:*:node.js:*:*, cpe:2.3:a:fastify:reply-from:*:*:*:*:*:node.js:*:*

Evidence & Provenance

3 public sources
cna.openjsf.orgSource recordnvd.nist.govSource recordgithub.comSource record

Linked by the query's stored exact CVE association. Review required tables and validation status before use.

Detection Hunting Query
Target: DeviceTvmSoftwareVulnerabilities•Defender XDR
Detect endpoints exposed to CVE-2026-33805
Purpose: Exposure assessment (Category: Exposure Check)Why linked: Query metadata names CVE-2026-33805
DeviceTvmSoftwareVulnerabilities| where CveId == "CVE-2026-33805"| project DeviceId, DeviceName, OSPlatform, OSVersion, SoftwareVendor, SoftwareName, SoftwareVersion, CveId, VulnerabilitySeverityLevel, RecommendedSecurityUpdate, RecommendedSecurityUpdateId| sort by VulnerabilitySeverityLevel desc
Schema Checked · Not runtime validatedSource: SecOps Signal deterministic template · Limited verificationStatic screening: Passed structure and schema checks; tenant execution is not verified.
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Correlated briefings

SecOps Signal surfaces public advisory facts only. A missing value means the source has not published it, not that your environment is unaffected. No tenant inventory is connected.