@fastify/reply-from vulnerable to connection header abuse enabling stripping of proxy-added headers

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Summary

CVECVE-2026-33805
StatePUBLISHED
Assigneropenjs
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-15 11:16:34 UTC
Updated2026-04-17 15:09:46 UTC
Description@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.

Risk And Classification

Primary CVSS: v4.0 9 CRITICAL from ce714d77-add3-4f53-aff5-83d477b104bb

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

EPSS: 0.000420000 probability, percentile 0.126870000 (date 2026-04-20)

Problem Types: CWE-644 | CWE-644 CWE-644: Improper Neutralization of HTTP Headers for Scripting Syntax

VersionSourceTypeScoreSeverityVector
4.0ce714d77-add3-4f53-aff5-83d477b104bbSecondary9CRITICALCVSS: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/C...
4.0CNACVSS9CRITICALCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
Present
Privileges Required
None
User Interaction
None
Confidentiality
None
Integrity
High
Availability
None
Sub Conf.
Low
Sub Integrity
High
Sub Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA @fastifyreply-from @fastify/reply-from affected 12.6.2 semver Not specified
CNA @fastifyreply-from @fastify/reply-from unaffected 12.6.2 semver Not specified
CNA @fastifyreply-from @fastify/http-proxy affected 11.4.4 semver Not specified
CNA @fastifyreply-from @fastify/http-proxy unaffected 11.4.4 semver Not specified

References

ReferenceSourceLinkTags
cna.openjsf.org/security-advisories.html ce714d77-add3-4f53-aff5-83d477b104bb cna.openjsf.org
github.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74... 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: FredKSchott (en)

CNA: mcollina (en)

CNA: UlisesGascon (en)

CNA: climba03003 (en)

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